research article ni-based ohmic contacts to n -type 4h-sic ...research article ni-based ohmic...

Research ArticleNi-Based Ohmic Contacts to n-Type 4H-SiCThe Formation Mechanism and Thermal Stability

A V Kuchuk123 P Borowicz14 M Wzorek1 M Borysiewicz1 R Ratajczak5

K Golaszewska1 E Kaminska1 V Kladko2 and A Piotrowska1

1 Institute of Electron Technology Aleja Lotnikow 3246 02-668 Warsaw Poland2V Lashkaryov Institute of Semiconductor Physics National Academy of Sciences of Ukraine Prospekt Nauky 41Kyiv 03680 Ukraine3Institute for Nanoscience and Engineering University of Arkansas West Dickson 731 Fayetteville AR 72701 USA4Institute of Physical Chemistry Polish Academy of Sciences Ulica Kasprzaka 4452 01-224 Warsaw Poland5National Centre for Nuclear Research Ulica Andrzeja Sołtana 7 05-400 Otwock Poland

Correspondence should be addressed to A V Kuchuk kuchukuarkedu

Received 2 November 2015 Revised 2 February 2016 Accepted 8 February 2016

Academic Editor Jan A Jung

Copyright copy 2016 A V Kuchuk et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices For then-type SiC Ni-based metallization is most commonly used for Schottky and ohmic contacts Many experimental studies havebeen performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explainthe Schottky to ohmic transition for NiSiC contacts In the present review we summarize the last key results on the matter andpost open questions concerning the unclear issues of ohmic contacts to n-type SiC Analysis of the literature data and our ownexperimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientationof silicide at the heterointerface (0001)SiC(013)120575-Ni

2Si Moreover we may conclude that only 120575-Ni

2Si grains play a key role

in determining electrical transport properties at the contactSiC interface Finally we show that the diffusion barriers with freediffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics

1 Introduction

The increasing demand for electronic devices capable offunctioning at high power and frequency levels under hightemperatures and in harsh environments is one of the mostsignificant issues of modern information society Moreoverenergy problems and environmental concerns due to globalwarming have generated a need for novel semiconductordevices for active electrical power management in areassuch as energy generation distribution and transport whereefficiency andhigh-temperature operations are of the essenceSilicon carbide (SiC) particularly the 4H polytype (4H-SiC)is one of the key candidates for application in such devicesowing to its excellent intrinsic properties which involve alarge bandgap (326 eV) high breakdown electric field (3 times106 Vcmminus1) high electron drift velocity (2 times 107 cm sminus1) good

thermal conductivity (49W cmminus1 Kminus1) and chemical inert-ness [1ndash3]

In order to take full advantage of the superior SiCproperties several challenges in material processing needto be overcome One of the most important issues is thequality and reliability of metalSiC electrical contacts This isespecially true for the ohmic contacts which are a part of anysemiconductor deviceThe issue of the ohmic contact forma-tion is primarily important because a high potential barrieris inclined to form at the interface between most metals andSiC which consequently results in low-current driving slowswitching speed and increased power dissipation Thus thefabrication of reliable and low-resistance ohmic contacts toSiC is still one of the most important problems that needaddressing This paper provides a comprehensive and criticalassessment of the fundamentals and practice of Ni-silicide

Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2016 Article ID 9273702 26 pageshttpdxdoiorg10115520169273702

2 Advances in Condensed Matter Physics

ohmic contacts to n-type 4H-SiC with an emphasis on high-temperature handling capability

There exist several review articles on contacts to SiC [4ndash6] however in the last few years many new peer-reviewedpapers on metalSiC contacts were published often contain-ing contradicting results and conclusions but no consensushas been reachedTherefore the aim of this work is to presentbriefly the last key results on the matter and to post openquestions concerning the unclear issues of ohmic contacts ton-type SiC

2 Ohmic Contacts to 4H-n-SiCState of the Art

For metal contacts to n-type 4H-SiC the electron affinity(119883119904) and work function of the metal (119882

119898) are the relevant

quantities determining the Schottky barrier height120593119861= 119882119898minus

119883119904 due to a sufficiently lowdensity of surface states in 4H-SiC

(sim1012 cmminus2 eVminus1) Thus according to the Schottky theorythe barrier height 120593

119861of a metal4H-n-SiC strongly depends

on the electron work function 119882119898of the metals Indeed as

is shown in Figure 1 the experimental results of metal4H-n-SiC contacts confirm this model [7ndash23]

As is well known a rectifying (Schottky) metal contactto n-type semiconductor is formed when the electron workfunction of the metal exceeds the electron affinity of thesemiconductor (119882

119898gt 119883119904) and the ohmic contact is formed

if119882119898le 119883119904 Since119882

119898for most metals exceeds the electron

affinity 119883119904of 4H-SiC (see Figure 1) the formation of ohmic

contacts to 4H-n-SiC is typically done by the deposition ofthe same metals as for the Schottky barriers however withsubsequent high-temperature annealing Such rapid thermalannealing (RTA) causes (i) the creation of a tunnel contactwhich consists of a thin barrier obtained by heavy doping ofthe semiconductor throughwhich carriers can readily tunneland (ii) the formation of new compounds which reduces thebarrier height and the width of the depletion region at themetal-semiconductor interface It should be noted that thispaper is focusedmainly on Si-face 4H-SiCmaterial Howeverthe SiC surface polarity (Si-face or C-face) and polytypes(3C 2H 6H etc) are important considerations for ohmiccontact formationThe polarity and polytypes can lead to thedifference in barrier height and interaction at the metalSiCinterface for the same metallization scheme [24] Thus bothof them strongly influence the electrical quality of the contact

On the basis of previous works [26ndash45] the commonprocesses in the reaction of metals with SiC can be identifiedas follows (i) SiC + refractory metals (Ti Ta W etc) rarrRTArarr carbides (TiC TaCWC etc) + silicides (TiSix TaSixWSix etc) + ternary phases (TiCSix TaCSixWCSix etc) (ii)SiC + othermetals (Ni Pd Pt etc)rarrRTArarr silicides (NiSixPdSix PtSix etc) + C

The fabrication of ohmic contacts to SiCmay be achievedusing various metallization schemes and for the n-typeSiC Ni and Ni-based contacts are most commonly usedThese contacts are formed by high-temperature annealingat temperatures in the range 900ndash1100∘C and their specificcontact resistance lies typically in the range 10minus4ndash10minus6Ωcm2

Electron work function Wm (eV)

Cu

CrW Ni

Ti

Al

Mo

Au

Pd Pt

Ir

20

18

16

14

12

10

08

06

04

02

0040 45 50 55

ExperimentalTheoretical (X4H-SiC

s = 36 eV)

Barr

ier h

eigh

t120593B

(eV

)

Figure 1 Experimental dependence of the barrier height 120593119861of

metal4H-n-SiC on the electron work function 119882119898of the metals

[7ndash23] Red curve-theoretical dependence according to the Schottkytheory (the electron affinity of 4H-SiC119883

119904= 36 eV [25])

[26ndash38] The physical properties of Ni and the main NixSi1minusxphases used in metallization scheme for SiC are listed inTable 1 [46ndash48]

Many experimental studies have been performed in orderto understand the mechanism of ohmic contact formationand different models were proposed to explain the Schottkyto ohmic transition however the final picture is still farfrom being complete Indeed in spite of a large numberof publications and progress in the study of Ni and SiCinteraction there are still many open questions connectedto the mechanism of contact formation and their reliabilityThere are different explanations in the literature concerningthe mechanisms of ohmic contact formation namely (i) theformation of silicides [35 39] or carbon precipitates [28 40](ii) inhomogeneity of the metalSiC Schottky barrier [41](iii) creation of carbon vacancies [42 43] or defect states[44] near the interface region and (iv) snowplow effect ofdopants in the SiC substrate [45] On the other hand ithas been commonly observed that the formation of ohmiccontacts is accompanied by the interfacial reaction andor SiCdecomposition

There is no doubt that Ni can very easily react withSiC forming a whole spectrum of nickel silicides dependingon the details of the ohmic contact fabrication process Onthe other hand there is strong evidence that the fabricationof silicides via a contact reaction of Ni with SiC or via adeposition of the specific silicide is not enough to produce anohmic contact with low specific resistance This is especiallytrue for Ni

2Si which was firstly proposed to be responsible for

the ohmic behavior but later shown to form Schottky barrierswith height of 162ndash175 eV [41] Also a question arises aboutthe fate of the remaining carbon which may segregate in thecontact region

Advances in Condensed Matter Physics 3

Table 1 Properties of Ni and Ni119909Si1minus119909

phases used in metallization scheme for SiC [46ndash48]

Phase Resistivity (120583Ω cm) Melting point (∘C) Enthalpy of formation(kJmol) Work function119882

119898(eV)

Ni 8minus10 1435minus1446 mdash 486 plusmn 02Ni2Si 20minus30 1255minus1318 132minus143 446

NiSi 10minus20 992 85minus90 435NiSi2

35minus50 981minus993 87minus94 mdash

As the silicide formation occurs at much lower tem-peratures (typically 400ndash600∘C [49 50]) than the transitionto ohmic behavior it has been suggested that a formationof an interfacial graphite layer is responsible for the ohmiccontact formation This hypothesis was supported by theobservation of ohmic behavior of graphitized carbon on SiC[51] On the other hand it has been shown that [52] if evenelemental C atoms may be present at the semiconductor-silicide interface at low temperatures that is when silicideforms the subsequent high-temperature treatment neces-sary for ohmic contact formation activates carbon atomsto out-diffuse towards the top surface of the silicide Thisobservation has led to a hypothesis that carbon out-diffusionproduces C vacancies below the contact which act as donorsfor electrons and increase the net electron concentrationbelow the contact thus reducing the barrier thickness Whilethe redistribution of interfacial carbon after silicide formationand its movement from the interface towards the contactsurface was proven by Calcagno et al [53] the DLTS mea-surements were not able to reveal the presence of a donorlevel related to 119881

119862 that is one located at 05 eV below the

conduction-band edge [31] Consequently it seems that therole carbon plays in ohmic contact formation is still unclear

Two problems related to the creation and structuralevolutions of carbon in SiC-based ohmic contacts are dis-cussed in the literature (i) what mechanism is responsible forcreation of carbon structure (ii) location of carbon specieson theNi-silicideSiC interface inside silicide layer or on freesilicide surface

Thermal decomposition of silicon carbide results in thecreation of amorphous carbon (a-C) The a-C layer appear-ing due to thermal 4H-SiC decomposition was alreadyobserved by means of cross-sectional transmission electronmicroscopy [54] The mechanism of reaction triggered bythermal decomposition of SiC has a complex character Itincludes the diffusion of carbon from the SiC interface andmetal atoms (Ni) towards this interface [55] This decom-position of silicon carbide is accompanied by the creationof Ni-silicides The solubility of carbon and silicon atoms insilicon carbide is much lower than in Ni-silicide Because ofthis the reaction triggered by decomposition of SiC takesplace in the layer deposited on silicon carbide [56] Themobility of carbon atoms in silicide is better than themobilityof silicon atoms [56] Because of this the thermal decom-position of SiC covered by Ni-layer results in formation ofsilicide and the escape of carbon atoms from SiCsilicideinterface The complexity of the interaction between SiC andmetal is also the result of the number of parameters that

influence the reaction The thickness of metal layer is oneof the important factors determining the structure of carboncreated during the decomposition of SiCThe investigation ofinteraction between 6H-SiC and Ni as a function of Ni-layerthickness showed the following [57] (i) for a very thin Ni-layer (04 nm) the homogeneous carbon film appears afterdecomposition (ii) for Ni-layer thickness in the range 16ndash96 nm carbon flakes appear the lateral dimensions of flakesnot greater than 200 nm and their thickness in the range5ndash100 graphene monolayers (iii) for a thickness of Ni-layerabove 50 nm the carbon structure is changed to hillocks

In view of the fact that the products of reaction betweenNi and SiC at the temperature of ohmic contact formation(sim1000∘C) are mainly Ni

2Si and C their role in the mecha-

nism of ohmic contact formation needs further investigationIn this work going further and clarifying in more detail theformation of Ni-based ohmic contact to 4H-n-SiC we haveinvestigated the influence of the layer sequence thicknessand temperature regime on the electrical and structuralproperties for NiSi contacts to 4H-n-SiC Furthermore thefabrication of low-resistivity ohmic contacts to SiC is notsufficient for application to SiC-based devices due to theirusage in harsh environments and at elevated temperaturesHere the investigation of the reliability for example thermalstability of the contacts is needed Therefore reliability testswere performed and are also presented in this work

3 Experimental

31 Sample Preparation n-type (sim2 times 1017 cmminus3) Si-face 4H-SiC(0001) bulk wafers and n-type (sim1 times 1019 cmminus3) Si-face4H-SiC(0001) epitaxial wafers (sim297 120583m thick) from CreeResearch Inc were used Before the deposition of the con-tacts the surface was chemically cleaned by the followingsteps (i) degreasing in hot organic solvents (trichloroethy-lene methanol and acetone) (ii) etching sequentially for10min in hot solutions of NH

4OH H

2O2 H2O = 1 1 5 at

65∘C and H2O2 HCl H

2O = 1 1 5 at 70∘C and (iii) etching

for 2min in buffered HF (HF NH4F H2O = 2 7 1) Before

each step the samples were rinsed in deionized water andblown dry using nitrogen

Ni Si and Au thin films were deposited by magnetronsputtering from Ni Si and Au 4N pure cylindrical targetsin an Ar plasma Ternary Ta-Si-N diffusion barriers for con-tact reliability studies were prepared by reactive magnetronsputtering of a highly pure Ta

5Si3target in an Ar-N

2plasma

The deposition parameters were as follows the gas flow rateratio during sputtering was ArN

2= 15 the total gas pressure


was 06 Pa the RF power was 250WThe resistivity measuredby the four-point probe of a 100 nm thick Ta

35Si15N50

filmwas 1mΩ cm The details of the heat treatment and aging arepresented in Section 41

32 Sample Characterization The electrical characterizationof the contacts involved measurements of current-voltage(I-V) characteristics and of the specific contact resistance(119903119888) I-V characteristics were measured by Keithley 2400

SourceMeter using an automated setup A circular trans-mission line model (c-TLM) method was used to measure119903119888 The c-TLM pattern prepared by lift-off photolithography

consists of inner contact pads with a diameter of 100120583m anda metallized area separated by rings with a space of 10 20 3045 and 60 120583m The phase composition of the contacts wasinvestigated by X-ray diffraction (XRD) using Philips XrsquoPert-MPD diffractometer with a Cu K

120572radiation source The

depth profile of the elements in the contacts was examinedby Rutherford backscattering spectrometry (RBS) using a17MeV He+ beam The contactSiC interface was observedby cross-sectional transmission electron microscope (TEM)JEM-200CX and high-resolution TEM (JEOL JEM-2100)The NanoScope IIIa atomic-force microscope (AFM) andPhilips XL-30 scanning electron microscope (SEM) wereused to study the surface morphology of the contact struc-tures

The properties of carbon species were investigated bymeans of micro-Raman spectrometer MonoVista 2750iSince 119863 and 119866 carbon bands are rather broad their widthsare of the order of 10 cmminus1 and the grating with 1800 groovesmmwas usedThe spectral resolution SpectraPro 2750i spec-trograph with used grating was good enough to record trueshapes of carbon bands The range of Raman shift recordedduring single measurement was large enough to detect bothcarbon bands (D and G) at the same time As excitationgreen line (120582 = 488 nm) from Ar+ laser (Innova 90C FREDCoherent Inc USA) was used the power of excitation wasset below 1mW on the sample in order to avoid side effectscaused by absorption The measurements were performedwith irradiation of both sides of the samples The measure-ments were done in the range of Raman shift from about1200 cmminus1 to about 1800 cmminus1 This range of frequenciescorresponds to the main Raman bands of graphite Thespectra measured at the side of the samples covered withNiSi sequence of layers are treated as region of interest (ROI)spectra and they will be analyzed in this work The spectrarecorded from the side not covered with NiSi sequence oflayers are treated as a reference The reason for measuringthe reference spectra is the occurrence of second-orderRaman spectra of 4H-SiC [58] and 119863 and 119866 carbon bandsin the same range of Raman shift The irradiation timenecessary to acquire the ROI spectra was long in particularit was in the range between 50 and 60 minutes No traces ofsecond-order Raman scattering of 4H-SiC were observed inROI spectra It means that second-order Raman scatteringcoming from 4H-SiC is below limit of detection in the case ofmeasurements obtained from the side of the samples coveredwith NiSi sequence of layers The reference Raman spectraare not presented in this work

Since the intensities of 119863 and 119866 carbon bands wereweak and the signal-to-noise ratio was not very good themeasurements in the range of Raman shift corresponding tothe position of the overtone of119863 band were not performed

In order to obtain precise information about 119863 and 119866carbon bands ROI Raman data were analyzed by meansof mathematical reconstruction of the spectra with sumof Gaussian functions Applied procedure was described indetail in previous paper [59]

4 Results

41 NiSi Ohmic Contacts to 4H-n-SiC BulkWafers Optimiza-tion of Layer Thickness Sequence and Temperature RegimeIn order to optimize the NiSi-based metallizations forapplication as ohmic contacts to n-SiC NiSi multilayersof different layer thicknesses and Ni-Si sequences werefabricated The thicknesses of the Ni and Si layers were setto yield chemical compositions of the Ni-Si mixture equal tothe stoichiometries of Ni-rich Ni

2Si NiSi and Si-rich NiSi

2

in the (i) (ii) and (iii) series respectively and as such thethicknesses were as follows 66 nm Ni and 60 nm Si in series(i) 45 nm Ni and 100 nm Si in series (ii) and 27 nm Ni and100 nm Si in series (iii) Furthermore in the frames of eachseries two sets of samples with different Ni-Si sequences wereprepared In the first Si was the first deposited layer on thesubstrate (denoted as FL-Si) and in the second Ni was thefirst deposited layer (FL-Ni) Thus six different sample setswere fabricated

The films were sputter-deposited on n-type (sim2 times

1017 cmminus3) 4H-SiC bulk wafers The as-deposited sampleswere first annealed at 600∘C (N

2 15min) when the nickel

silicides phases (Ni2Si NiSi and NiSi

2) are formed according

to previous XRD results [35] Subsequently the samples wereannealed in temperatures rising from 800 to 1100∘C (N

2

3min) to study ohmic contact formationThe electrical properties for all NiSimultilayermetalliza-

tions before and after annealing are summarized in Figure 2Nonlinear I-V characteristics were observed for all as-deposited metallizations and for metallizations annealed upto 1000∘C After further annealing up to 1100∘C the I-V char-acteristics for the NiSi

2n-SiC contacts do not change con-

siderably and quasi-linear I-V characteristics are observedfor the NiSin-SiC contacts but they remain nonohmic TheSchottky-ohmic transitionwas observed only for theNi

2Sin-

SiC contacts after annealing at temperatures ge1050∘C For theNi2Sin-SiC contacts with FL-Si a transition to a quasi-linear

I-V characteristics and the formation of ohmic contacts withspecific contact resistances 119903

119888sim 45 and sim58times 10minus4Ω cm2

were observed after annealing at 1050 and 1100∘C respec-tively For the Ni

2Sin-SiC contacts with FL-Ni nonlinear

I-V characteristics after annealing at 1000 and 1100∘C wereobserved and the formation of ohmic contact with 119903

119888sim 55 times

10minus4Ω cm2 was registered after annealing at 1050∘C In order

to study the structure evolution during the formation of theNi2Sin-SiC ohmic contact as well as the influence of the type

of the interfacial layer on the substrate (ie FL-Si or FL-Ni)on contact formation RBS-depth profiling was performed


I(A

)

U (V)

Ni2Si (NiSi tNitSi minus 11)

As-deposited800∘CN25min950∘CN23min1050∘CN23min

600∘CN215min900∘CN25min1000∘CN23min1100∘CN23min

03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2

1050∘C rc sim 55 times 10minus4 Ω cm2

(a) FL-Ni

I(A

)

U (V)

Ni2Si (NiSi tNitSi minus 11)03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2





(b) FL-Si

I(A

)

U (V)minus2 minus1 0 1 2

003

002

001

000

minus001

minus002

NiSi (NiSi tNitSi minus 055)



(c) FL-Ni

I(A

)


003

002

001

000

minus001

minus002

minus003




(d) FL-Si

I(A

)


0004

0003

0002

0001

0000

minus0001

minus0002

minus0003

NiSi2 (NiSi tNitSi minus 027)



(e) FL-Ni

I(A

)


0015

0010

0005

0000

minus0005

minus0010




(f) FL-Si

Figure 2 Electrical properties of NiSi multilayer contacts with different interfacial layer (Si FL-Si or Ni FL-Ni) and thickness ratio (119905Ni119905Si)to n-type (sim2 times 1017 cmminus3) 4H-SiC bulk wafers versus annealing temperature


SiSiC SiNi2Si

NiRB

S yi

eld

(au

)

Channel numbern-SiCNi2Si (FL-Si)

400 500 600 700

18

16

14

12

10

8

6

4

2

0

As-deposited600∘C1050∘C1100∘C

(simulation)(simulation)(simulation)(simulation)

(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)

Figure 3 RBS spectra for as-deposited and annealed at 600∘C 1050∘C and 1100∘C contacts (a) n-SiCNi2Si with FL-Si (b) n-SiCNi

2Si with

FL-Ni [26]

RBS profiles for the Ni2Sin-SiC contacts were measured

after deposition and after subsequent annealing up to 1100∘CThe spectra are shown in Figures 3(a) and 3(b) for sampleswith FL-Si or FL-Ni respectivelyThe changes in the RBS pro-files after annealing at 600∘C for bothmetallization sequencesindicate only a solid state reaction between the Ni and Sisingle layers and no reactions at the contactSiC interfacetake place Simulations of these spectra performed using theSIMNRA code [60] confirm the formation of sim95 nm thickuniform mixtures with the atomic ratio of Ni Si sim 2corresponding to stoichiometric Ni

2Si as it was showed by

XRD phase analysis [26] Annealing of both metallizationsequences at 1050∘C does not induce significant changes inthicknesses or compositions of the metallizations indicatingthermal stability of the Ni

2Si phase on SiC substrates as

previously reported [33 61 62] However the very smallchange in the slopes of the RBS signals corresponding toNi (Ni

2Si) and Si (SiC) measured for the metallizations

annealed at 600 and 1050∘C indicates a small reorganizationat the metallizationSiC interface at a maximum distanceestimated at sim20 nm SIMNRA simulations show that forthe Ni

2Sin-SiC metallization sequences with FL-Si annealed

at 1050∘C sim5 at of Si and C atoms out-diffused fromthe SiC substrate and sim10 at of Ni atoms diffused intoSiC whereas for sequences with FL-Ni sim10 at of Si andC out-diffused from SiC and sim20 at of Ni diffused intoSiC It is important to mention that this minute interactionbetween Ni

2Si and n-SiC after annealing at 1050∘C correlates

well with the Schottky-ohmic transition of contacts Furtherannealing at 1100∘C enhanced interdiffusion at the Ni

2SiSiC

interface The comparison of the RBS profiles of the twometallization sequences annealed at 1100∘C reveals a more

pronounced reaction for the Ni2Sin-SiC contacts with FL-

Ni (sim160 nm in-depth penetration of Ni into SiC) than forthe contacts with FL-Si (sim40 nm in-depth penetration of Niinto SiC)This result correlateswith the observed degradationof the electrical properties of the Ni

2Sin-SiC contacts when

nonlinear I-V characteristics appear for the FL-Ni sequencesand 119903119888decreases for the FL-Si sequences

The analysis of the obtained experimental results indi-cates that in order to form anNi-Si-based ohmic contact to n-SiC the chemical composition of theNi-Si layer has to be care-fully controlled Moreover the formation of any Ni-silicidesat low temperature is not sufficient to obtain ohmic contactsto n-SiC which is in agreement with the results reportedpreviously [8 42 63] The ohmic contacts were found tobe formed only by the Ni

2Si phase after high-temperature

annealing (gt1000∘C) via a small scale interfacial reaction ofNi2Si with SiC which probably leads to modification of the

properties of the SiC surface The reason why the NiSi andNiSi2phases do not form ohmic contacts to n-SiC even after

annealing at 1100∘C is not clear However two approachesto explain this can be suggested based on the differencebetween work functions andor melting temperatures of Ni-silicides The compositional-induced work function tuningof Ni-silicides was previously observed and a decrease ofthe work function by sim07 eV was shown between Ni-richand Si-rich Ni-silicides [48] Thus the Schottky barrier to n-SiC lowers with the transition from Ni

2Si to NiSi

2contacts

Moreover the formation of NiSi and NiSi2ohmic contacts

to n-SiC with a high doping concentration (1 times 1020 cmminus3)after annealing at 950∘C (N

2 3min) was previously reported

[64]Therefore the nonohmic behavior of the NiSi and NiSi2

contacts reported herein can be explained by the low doping


concentration (sim1017 cmminus3) of n-SiC and the low meltingtemperature of about 990∘C for NiSi and NiSi

2bulk materials

(compared to sim1318∘C for Ni2Si) [46] The instability of the

NiSi and NiSi2phases on SiC may result in Ni segregation

after high-temperature annealing In addition the excess Siatoms from Ni-silicides probably lead to dopant deactivationvia cluster formation or ldquoneutralizingrdquo of the donor atomsTherefore only a specific reaction at region near the metal-lizationn-SiC interface can enhance significantly the electriccurrent through the contact This also explains the morepronounced degradation of the electrical properties of theNi2Sin-SiC ohmic contacts with FL-Ni after annealing at

1100∘CAs a result we were able to optimize the sequence

thickness and temperature regime for the formation ofohmic NiSi contacts to 4H-n-SiC Annealing of the NiSimultilayers (119905Ni119905Si sim 11) at 600∘C led to the formation ofstoichiometric silicide Ni

2Si Minimal specific contact resis-

tances (sim45times 10minus4Ω cm2) were obtained for such Ni2Sin-

SiC contacts with FL-Si after annealing at 1050∘C Forconvenience the Ni

2Si metallizations with FL-Si are denoted

as Ni2Si below in the text

42 Ni versus Ni2Si Ohmic Contacts to 4H-n-SiC Bulk Wafers

In order to better understand the formation mechanism ofNi-based ohmic contacts to n-SiC a comparative study of Niversus Ni

2Si contacts on the same n-type (sim2 times 1017 cmminus3)

4H-SiC bulk wafers annealed at similar temperatures wascarried out The properties of the as-deposited and annealedcontacts are summarized inTable 2 As it was in the case of theNi2Sin-SiC contacts nonlinear I-V characteristics for Nin-

SiC contacts were observed after annealing at temperaturesbetween 600∘C and 1000∘C [38] The Nin-SiC ohmic con-tacts are formed only after annealing at 1050∘C The specificcontact resistance 119903

119888 was equal to sim4times 10minus4Ω cm2 which

is comparable to the value of 45times 10minus4Ω cm2 obtained forNi2Sin-SiC ohmic contacts annealed at 1050∘C In spite of

similar electrical properties of Ni and Ni2Si contacts signif-

icant differences were observed in their structural properties(see Table 2) For the Nin-SiC contacts the metallizationthickness increases by a factor of sim2 and sim25 and thesurface roughness increases by a factor of sim14 and sim20 afterannealing at 600∘C and 1050∘C respectively For the Ni

2Sin-

SiC contacts the metallization thickness remains unchangedand only the surface roughness increases by a factor of sim4 after annealing at 1050∘C In order to understand thesedifferences between Ni and Ni

2Si contacts XRD and RBS

methodswere applied to study the structural properties of theNin-SiC contacts

XRD and RBS profiles for Nin-SiC contacts after depo-sition and annealing at 1050∘C are shown in Figure 4 Fromthe XRD spectra (Figure 4(a)) we may conclude the fol-lowing (i) for the as-deposited contact only the Ni (111)diffraction peak was detected thus indicating the texture ofthe deposited film (ii) for the contact annealed at 1050∘Conly the (013) and (020) peaks of the 120575-Ni

2Si orthorhombic

phase were detected thus indicating a thermally activatedinteraction between Ni and SiC From the analysis of the RBS

profiles (Figure 4(b)) we can deduce that annealing at 1050∘Cenforces diffusion of Ni atoms towards the SiC substrate andmigration of Si and C atoms towards the surface Severalwell-distinguished plateaus in the RBS signals for Ni and Siindicate the formation of several intermetallic compoundsSIMNRA simulations yielded the following film structurefrom the top surface to the substrate firstly a 25 nm thicklayer at the atomic ratio of Ni Si sim 2 containing sim12 at ofC next a 60 nm thick Ni

2Si sublayer enclosing sim26 at of

C subsequently a 35 nm thick mixture of sim32 at of Ni sim19at of Si and sim49 at of C and finally near the interfacea 16 nm thick film of NiSi silicide with a smaller content ofsim33 at of C Significant diffusion of Ni is observed intoSiC with sim17 at of Ni estimated at sim40 nm in depth Thechemical composition of Ni Si sim 2 in the 85 nm thick toplayer correlates well with 120575-Ni

2Si phase identified by XRD in

the sampleThe formations of nickel silicides and carbon atoms in

annealed Nin-SiC contacts are consistent with previouslyreported results [33 61] Thus the observed increase ofmetallization thickness in annealed Nin-SiC contacts (seeTable 2) can be explained by these diffusion processes Itshould be noted that the increase of metallization thicknesseven at 600∘C indicates an interaction between Ni and SiCwhich is consistent with the previously reported formationof Ni-silicides at this temperature [12] However in spite ofthe reaction between Ni and SiC and the formation of Ni-silicides at just 600∘C the contacts remain rectifying up to1050∘C Moreover it becomes evident that the formation ofthe Ni

2Si phase either by an interaction between Ni and SiC

by a solid state reaction between Ni and Si single layers onn-SiC or by a deposition of Ni

2Si layers [62] is not sufficient

for the formation of an ohmic contact to n-SiC In all of thecases a specific interaction between themetallization and SiCis needed to change the properties of the contactSiC near-interface region which takes place only after annealing athigh temperature (sim1000∘C)

This is the reason why the Ni2Sin-SiC and Nin-SiC

ohmic contacts have similar 119903119888sim 4times10

minus4Ω cm2 after anneal-

ing at 1050∘C However the quality of the Ni2Si metallization

formed as a result of the annealing of NiSi multilayers has agreat advantage over the one formed by the annealing of theNi single layer namely one can introduce a ldquopassivatingrdquo thinSi film as the first layer (FL-Si) deposited on the SiC surfaceas mentioned in Section 41

43 Microstructure and Interfacial Properties of Ni2Sin-SiC

Contacts In order to investigate the reaction at themetalliza-tionSiC interface leading to the formation of ohmic contactsXRD AFM and TEM techniques were applied to studythe microstructure and interfacial properties of Ni

2Sin-SiC

contactsThe results of XRDmeasurements performed in a Bragg-

Brentano geometry which probes through the depth ofmetallization are shown in Figure 5(a) For the as-depositedNi2Sin-SiC contact only the (111) diffraction peak from

textured polycrystalline Ni was detected For the contactannealed at 600∘C the (013) and (020) peaks correspondingto the 120575-Ni

2Si orthorhombic phase and the (300) peak


Table 2 Properties of Ni and Ni2Si contacts to n-type (sim2 times 1017 cmminus3) 4H-SiC bulk wafers versus annealing temperature

Annealing temperature n-SiCNi n-SiCNi2Si

119903119888(times10minus4Ω cm2) lowast

119877 (nm) lowastlowast119863 (nm) 119903

119888(times10minus4Ω cm2) 119877 (nm) 119863 (nm)

As-deposited I-V nonlinear sim3 sim86 I-V nonlinear sim3 sim110600∘C15min I-V nonlinear sim40 sim186 I-V nonlinear sim4 sim1001050∘C3min 4 plusmn 2 sim58 sim225 45 plusmn 1 sim12 sim108Peak-to-valley height (lowast119877) on the 25120583m surface scan length and thickness (lowastlowast119863) of metallization measured by TENCOR 120572-Step Profiler

n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102

As-deposited1050∘C

(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C

SiNi1minus119909Si119909

As-deposited (simulation)(simulation)

(b)

Figure 4 XRD (a) and RBS (b) spectra for as-deposited and annealed at 1050∘C n-SiCNi (85 nm) contacts

corresponding to the Ni31Si12hexagonal phase are observed

Taking into account that no trace of the Ni or Si peaksappears in the XRD pattern we conclude that a full thermallyactivated interaction between Ni and Si single layers tookplace which is consistent with RBS results (Figure 3(a)) Forthe contact annealed at 950∘C only the (013) and (020)peaks of the 120575-Ni

2Si phase were detected The disappearance

of the peak corresponding to the Ni31Si12

phase indicatesa full transformation of other Ni-silicides into the 120575-Ni

2Si

orthorhombic phase Moreover as the intensity of the (013)peak is the highest we can deduce a strong texturizationof the 120575-Ni

2Si grains For the contact annealed at 1050∘C

the (020) peak disappears leaving only the (013) peak indi-cating full grains texturization However after annealing at1100∘C degradation of the (013) structure is visible througha significant lowering of the intensity of the (013) line anda reappearance of the (020) peak as well as the appearanceof a new peak (2120579 asymp 4774∘) close to the (022) reflection ofthe Si-rich NiSi

2phase This indicates the strong interaction

at the metallizationSiC interface that was also observed byRBS (Figure 3(a)) Figure 5(b) shows the intensity ratio of the(013) to (020) peaks (119868

013119868020

) and FWHM (full width halfmaximum) for the 120575-Ni

2Si (013) diffraction peak in the func-

tion of annealing temperature A dashed horizontal line onthe chart corresponds to 119868

013119868020

sim 25 which is a theoretical

value for a fully polycrystalline nontextured film The evo-lution of the texture can be traced from this figure asfollows after annealing at 600∘C the film is (013) texturedand the preferred orientation is getting stronger with eachsubsequent annealing at temperatures up to 1050∘CHoweverafter annealing at 1100∘C the ratio falls below 25 suggestinga random orientation of the Ni

2Si crystallites and destruction

of the texture It is clearly seen that the changes of 120575-Ni2Si (013) texture with annealing temperature correlate well

with change of FWHM for 120575-Ni2Si (013) which is justified

since the latter is sensitive to the perfection and size ofcrystallites The texturing of the Ni

2Si phase with increasing

of annealing temperature was also observed previously forNin-SiC contact [65]

The surface morphology of the Ni2Sin-SiC contacts

before and after annealing measured by AFM is shown inFigure 6The as-deposited sample (Figure 6(a)) has a smoothsurface (with peak-to-valley difference 119867 sim 6 nm) wheredensely packed Ni grains of average size of 15 nm can beresolved Annealing at 600∘C causes 119867 to increase to 13 nmand the diameter of the grains to 20 nm (Figure 6(b)) Ona larger area 30 nm high precipitates are visible originatingfrom the interaction between Ni and Si single layers as shownearlier in RBS andXRDmeasurements A strongmorphology


XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102

120575-Ni2SiNiNiSi2Ni31Si12

42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)

Annealing temperature (∘C)

055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)

Figure 5 (a) XRD patterns of Ni2Sin-SiC contacts before and after annealing at 600 950 1050 and 1100∘C (b) Ni

2Si texture (119868

013119868020

) andFWHMof (013)Ni

2Si peak in XRD patterns versus annealing temperature (horizontal dash lines show the theoretical value for 119868

013119868020

in theabsence of texture) [66]

50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)

Figure 6 AFM images of surface topology of Ni2Sin-SiC contacts before (a) and after annealing at 600∘C (b) 1050∘C (c) and 1100∘C (d)119867

surface heights ranging

change is observed for the contact after annealing at 1050∘C(Figure 6(c)) The well-defined blocks as wide as sim250 nmindicate a recrystallization of the Ni

2Si phase which cor-

relates well with the XRD results (Figure 5) Moreovertheir spatial arrangement indicates the preferentially orientedgrowth Small diameter pores of 40 nm depth can be seen

between these blocks A subsequent annealing at 1100∘Cdegrades the morphology even more (Figure 6(d)) 140 nmdeep pores appear in the film indicating local expositionof the SiC substrate which was also indicated in SEMmeasurements [67] The pores have diameters ranging from05 to 3 120583m and a density sim 01120583m2


c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)

Figure 7 Results obtained from plan-view specimen of the contact annealed at 600∘C (a) plan-view TEMmicrograph (b) map representingXEDS nickelsilicon signal ratio obtained for the same area as TEM image presented in (a) (c) selected area diffraction pattern obtained forthe area marked with the circle in (a) and (b) (d) NBD pattern obtained for a grain located in the area with small grains

TEM investigations [67] of the contact annealed at 600∘Cshowed that the metallizationSiC interface remains smootheven after a reaction between the Ni and Si single layersand the formation of a uniform polycrystalline layer (95 nmthick) this correlates well with the XRD and RBS results(Figures 3(a) and 5(a)) A plan-view TEM micrograph fromthe sample annealed at 600∘C is presented in Figure 7(a)When considering grain sizes the two types of grains can bedistinguished Grains of first type have sizes above 100 nmwhile the second-type grains are smaller with sizes upto about 50 nm Distribution of chemical elements in thesame area was investigated with X-ray energy dispersivespectrometry (XEDS) Figure 7(b) represents the map ofNi distribution divided by the map of Si after performingGaussian averaging procedure on each map Areas of twodifferent chemical compositions (NiSi X-ray signal ratio)are clearly visible From comparison of Figures 7(a) and7(b) it can be concluded that ldquoredrdquo areas in Figure 7(b)which are the areas with higher NiSi XEDS signal ratioare the areas with large grains and ldquogreenrdquo regions with

lower NiSi ratio are the regions with small grains The circlemarked in Figures 7(a) and 7(b) indicates the position ofselected area diffraction (SAED) aperture which was usedto obtain diffraction pattern presented in Figure 7(c) Thechosen area was in the ldquoredrdquo region of the XEDS NiSi map(Figure 7(b)) that is in the area of higher NiSi XEDS signalratio and large grains The grains within the selected regionhad been oriented in the zone-axis prior to diffraction patternacquisition The acquired diffraction pattern indicates thecrystal structure of Ni

31Si12

phase (Figure 7(c)) Nanobeamdiffraction (NBD) pattern obtained from a grain located inthe area with small grains is presented in Figure 6(d) Thepattern indicates the crystal structure of Ni

2Si phase TEM

analysis showed that in the sample annealed at 600∘CNi31Si12

and Ni2Si grains are present However the presence of small

grains of other phases is also possibleThe sizes of theNi31Si12

grains are significantly larger from other grainsAn exemplary cross-sectional TEM micrograph from

the contact annealed at 600∘C and subsequently at 1050∘Cis presented in Figure 8(a) The metallization consists of


1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)

Figure 8 Cross-sectional (a c) and plan-view (b d) TEM micrographs obtained from NiSiNiSi4H-SiC contact annealed at 600∘C andsubsequently at 1050∘C (a b) or 1100∘C (c d) Exemplary voids are indicated with number 1 and discontinuities of the layer are indicated withnumber 2

large columnar grains and voids (probably empty spacesmarked with number 1 in Figure 8) [67ndash69] the height ofthe grains determines the contact thickness An exemplaryplan-view TEM obtained for the same contact is presentedin Figure 8(b) It may be concluded that during high-temperature annealing the grains dimensions have increasedcontrary to the sample annealed at 600∘C no small grains areobserved Cross-sectional and plan-view TEM micrographsfrom the contact annealed at 600∘C and subsequently at1100∘C are presented in Figures 8(c) and 8(d) respectivelyLayer discontinuities (pores) can be also distinguished inFigures 8(b) and 8(d) The possible formation mechanism ofthe observed voids and layer discontinuities was discussed in[69] and the method for their elimination was proposed

In the samples annealed at 1050∘Cor at 1100∘Cmainly theNi2Si phase was detected No Ni

31Si12grains were observed

XEDS investigations revealed that beside Ni2Si also some

areas with higher Si content are present [70] The metastablehigh-temperature phase denoted in the literature as 120579-Ni

2Si

or hexagonal Ni3Si2 was detected in these regionsTheNi Si

ratio in this phase can continuously change to some extentHowever it should be noted that only small part of the sampleis investigated in TEM therefore some additions of otherphases are possible

Based on the results reported above one may con-clude that in the investigated contacts mainly the 120575-Ni

2Si

grains contribute to the electrical transport properties atthe contactSiC interface The interface between the 4H-SiC and the 120575-Ni

2Si was investigated using cross-sectional

high-resolution TEM For the contact annealed at 600∘C(Figure 9(a)) an amorphous region near the interface isvisible The high-temperature annealed (1050∘C) contact hasa more ordered interface (Figure 9(b)) that is atomicallyabrupt and no contaminations or transition regions can beresolved Moreover in the investigated area the absence of

graphitic carbon at the interface is evident and the Ni2Si

layer is textured The silicide lattice fringes have spacing ofsim199 A close to the spacing of the (013) planes of 120575-Ni

2Si

(sim1982 A) They are parallel to the (0001) planes of the 4H-SiC indicating the orientation relationship (0001)SiC(013)120575-Ni2Si This is consistent with the XRD results presented

above (Figure 4(a)) Similar results were observed previously[70] for NiAl contacts to n- and p-type SiC after annealing at1000∘C when a polycrystalline 120575-Ni

2Si(Al) grain was found

to have grown with (013) planes parallel to the (0001) plane ofthe SiC substrate

44 Electrical Properties of Ni2Si Contacts to 4H-n-SiC Epitax-

ial Wafers As the TLM method requires that the measuredcontact should be placed on a thin film of the semiconductorand not on bulk in order to obtain its true electrical prop-erties Ni

2Sin-SiC samples on n-type (sim1 times 1019 cmminus3) 4H-

SiC epitaxial wafers were fabricated specially for this purposeThe contacts were first annealed at 600∘C (N

2 15min) and

subsequently in temperatures rising from 900∘C to 1100∘C(N2) and time rising from 3 to 12min For comparison pure

Ni contacts were fabricated on the same 4H-n-SiC epitaxialwafers and annealed at similar temperatures for 3min

The electrical properties of Ni and Ni2Si contacts to 4H-

n-SiC epi-layers before and after annealing are shown inFigure 10 The Nin-SiC ohmic contacts are formed alreadyafter annealing at 900∘C (3min) On the other hand theNi2Sin-SiC contacts become ohmic only after 12min of

heat treatment at this temperature The influence of heattreatment time on the value of 119903

119888for Ni

2Sin-SiC ohmic

contacts annealed at a relative low temperature (900∘C) aswell as at a high temperature (1100∘C) is evident This can berelated with ordering changes and a reactioninterdiffusion atthe contactSiC interface after annealing at 900∘C and 1100∘CrespectivelyThe changes in 119903

119888with annealing temperature for


Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)

Figure 9 Cross-sectional high-resolution TEM images of interfacial region between the 4H-SiC substrate and the Ni-silicide after annealingat 600∘C (a) and subsequently at 1050∘C (b) [71]

Annealing temperature (∘C)900 950 1000 1050 1100

10minus3

10minus4

10minus5

r c(Ω

cm2 )

Nin-SiCNi2Sin-SiC3min3min

6min12min

Figure 10 Specific contact resistances (119903119888) of Ni and Ni

2Si ohmic

contacts to n-type (sim1 times 1019 cmminus3) 4H-SiC epiwafers versus anneal-ing temperaturetime

both contacts correlate well with the changes of texture sizeand perfection of the 120575-Ni

2Si phase as shown in Figure 11The

minimal specific contact resistances 119903119888sim 5 times 10

minus5Ωcm2 of

these contacts annealed at the optimal temperature (1000∘C)are lower than 119903

119888sim 5 times 10

minus4Ωcm2 of Ni and Ni

2Si ohmic

contacts to low doped (sim1017 cmminus3) bulk n-SiC annealed at1050∘C It should be noted that for both the epitaxial waferand bulk each step in the contact fabrication process wasrepeated identically (i) the chemical cleaning of the surface(ii) NiSi multilayers thicknesses and Ni-Si sequences Thusthe reason why 1000∘C annealing is the best for epitaxialwafer although 1050∘C is the best for bulk sample can beattributed to the properties of substrates (i) low dopingconcentration (1017 cmminus3) for 4H-SiC bulk wafer and highdoping concentration (1019 cmminus3) for 4H-SiC epitaxial layer(ii) better crystal quality of epitaxial layer The differencein the doping concentration leads to the difference in thespace charge region (the depletion width) for the contacts

Annealing temperature (∘C)600 1000 1100

120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4

Figure 11 Specific contact resistances (119903119888) of Ni

2Si4H-n-SiC ohmic

contacts and Ni2Si texture (119868

013119868020

) versus annealing temperature

The crystalline quality of the substrate can influence theinteraction between Ni

2Si and SiC and the homogeneity of

contact interface at nanoscale Based on this we can explainthe difference in optimal annealing temperature betweenbulk and epitaxial wafers for lowest contact resistance andbarrier height Moreover we think this is also the reasonthat for 4H-SiC epitaxial layer contact becomes ohmic afterannealing at 950∘C but for 4H-SiC bulk wafer only afterannealing at 1050∘C

In order to determine the relative importance of theelectron transportation mechanisms at the interface betweenthe contact and semiconductor it is necessary to calculate themagnitude of the Padovani-Stratton parameter 119864

00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)

where ℎ is Planckrsquos constant 119898lowast is the effective mass of theelectron in the semiconductor 120576 is semiconductor dielectricconstant and 119873

119889is the donor concentration The size of

11986400

with respect to 119896119879 gives an indication of the relativeimportance of field emission (FE 119864

00119896119879 ≫ 1) thermionic

field emission (TFE 11986400119896119879 sim 1) or thermionic emission


r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020

The literatureNin-SiCNi2Sin-SiC

Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)

Figure 12 (a) Calculated ohmic contact resistance (119903119888) as a function of the doping concentration (119873

119889) of 4H-n-SiC for various barrier heights

(120593119861)The lines represent the calculated dependences based on the TE and TFEmodelsThe points represent the experimental data for contacts

annealed at 950 1000 and 1050∘C for 3min as well as some data from [7ndash47] (b) Effective barrier height (120593119861) of Ni and Ni

2Si ohmic contacts

to n-type (sim1 times 1019 cmminus3) 4H-SiC epiwafers versus annealing temperaturetime

(TE 11986400119896119879 ≪ 1) [73] In our case (n-type 4H-SiC) and at

our maximum doping level of 1 times 1019 cmminus3 119898lowast = 0361198980

and 120576 = 9661205760 11986400

was found to be about 315meV Acomparison of 119864

00to the thermal energy 119896119879 shows

thermionic field emission to dominate (11986400119896119879 = 125) The

FE model is the dominant mechanism for the ohmic contactto a degenerated semiconductor

The barrier heights of the contacts after annealing wereestimated by comparing the theoretical andmeasured contactresistances Since the density of states in the conduction bandof 4H-SiC is gt1 times 1019 cmminus3 [74] samples used here were notdegenerated because of 119899 sim 1 times 10

19 cmminus3 Therefore wecalculated the theoretical curve for the carrier concentrationdependence of the specific contact resistance by using the TEand TFE models

According to the TE the specific contact resistance iscalculated by [72]

119903119888=119896119879

119902119860lowastexp(

120593119861

119896119879) (2)

where 120593119861is barrier height and 119860lowast (= 146A cmminus2 Kminus2 for 4H-

SiC [75]) is the Richardson constantAccording to the TFE the specific contact resistance is

calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where

119873119889is the donor concentration and 119873

119888is effective density of

states in conduction bandIn Figure 12(a) the theoretical specific contact resistances

119903119888of ohmic contacts to 4H-n-SiC are plotted as a function

of the doping concentration (119873119889) and barrier height (120593

119861)

ranging from 03 eV to 05 eV The quantitative agreement oftheoretical our experimental and previously reported valuesof 119903119888is evident The measured variation of 119903

119888for Ni and

Ni2Si ohmic contacts with annealing temperaturetime shows

different values of the effective barrier height (120593119861) as shown

in Figure 12(b) The minimal values of 120593119861sim 042 plusmn 03 eV for

Ni2Si(Ni)n-SiC ohmic contacts annealed at 1000∘C correlate

well with values of 120593119861sim 042 eV previously reported for Ni

contacts to n-type 4H-SiC annealed at 1100∘C [76]Thus the changes of 119903

119888and microstructure of 120575-Ni

2Si

phase with annealing temperature for Ni2Sin-SiC ohmic

contacts were correlated with the changes of effective barrierheight (120593

119861) at the contactSiC interface This explains the

similar electric properties of the Ni2Sin-SiC and Nin-SiC

contacts and high-temperature annealing (sim1000∘C) neededfor ohmic contact formation

45 The Role of SiC Decomposition in the Formation of Ni-Based Ohmic Contacts Figure 13 presents the data obtainedfor the Ni

2Sin-SiC contacts with FL-Si annealed at different

temperatures The signal presented in Figure 13(a) can bemodeled using a sum of three Gaussian functions The maincomponent has themaximumat 1587 cmminus1 and FWHMequalto 579 cmminus1 Two other Gaussian profiles have the maxima at


Inte

nsity

(au

)

Raman shift (cmminus1)


1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800

Experimental dataFitted functions

(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)

Figure 13 Raman spectra recorded for the Ni2Sin-SiC contacts with FL-Si after different thermal treatment (a) as-deposited (b)

600∘C15min (c) 950∘C3min (d) 1050∘C3min

1191 cmminus1 and 1707 cmminus1 and FWHM equal to 105 cmminus1 and81 cmminus1 respectively

In the case of the experimental data shown inFigure 13(b) four Gaussian functions are necessary toget proper shape of the spectrum The maxima of theGaussian functions have the following positions 1361 cmminus11476 cmminus1 1597 cmminus1 and 1714 cmminus1 The correspondingvalues of FWHM are equal to 61 cmminus1 215 cmminus1 91 cmminus1and 121 cmminus1

The data presented in Figures 13(c) and 13(d) require fiveGaussian profiles to obtain proper mathematical reconstruc-tion of the spectrumThree profiles can be recognized as rela-tively narrow and two others as broadThe first narrowGaus-sian component has the maximum placed at 1194 cmminus1 in thecase of the spectrum presented in Figure 13(c) and 1170 cmminus1for the spectrum shown in Figure 13(d) The corresponding

FWHM values are equal to 74 cmminus1 and 142 cmminus1 respec-tively The next narrow profiles are placed around 1366 cmminus1in the case of spectrum from Figure 13(c) and 1360 cmminus1for spectrum from Figure 13(d) The values of FWHM arealmost equal for both Gaussian profiles The exact values are47 cmminus1 and 48 cmminus1 for spectra fromFigures 13(c) and 13(d)respectively The third narrow profile has the maximum at1584 cmminus1 in the case of spectrum from Figure 13(c) and at1586 cmminus1 for Figure 13(d) The value of FWHM is in thecase of Gaussian function from Figure 13(d) much smallerin comparison with the same function from Figure 13(c)The FWHM of Gaussian profile from Figure 13(c) is equalto 51 cmminus1 The same parameter obtained for the spectrumpresented in Figure 13(d) is equal to 39 cmminus1 BroadGaussianprofiles can be divided into two pairsThe components of thefirst pair have the maxima placed between bands reproduced

Advances in Condensed Matter Physics 15In

tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613

Figure 14 Raman spectrum recorded forNin-SiC contact annealedat 1050∘C

by second and third narrow Gaussian functions The valuesobtained from fitting procedure are equal to 1522 cmminus1 and1469 cmminus1 for spectra from Figures 13(c) and 13(d) respec-tively Both Gaussian functions have large FWHM Theyare equal to 385 cmminus1 and 594 cmminus1 for profiles fromFigures 13(c) and 13(d) respectively The last pair is com-posed of Gaussian functions centered at 1703 cmminus1 in thecase of Figure 13(c) and at 1666 cmminus1 for Figure 13(d) Thecorresponding FWHM values are equal to 234 cmminus1 and404 cmminus1

Figure 14 presents the reference spectrummeasured for aNi-layer deposited on n-SiC substrate (Nin-SiC contact) andannealed at 1050∘CThe signal-to-noise ratio is in the case ofthis spectrummuch better in comparison with any spectrumfrom Figure 13 Six Gaussian functions are necessary forproper reconstruction of the spectrum The first profile hasthe maximum at 1474 cmminus1 and FWHM equal to 450 cmminus1The maximum of this profile is not given in the plot Thelast Gaussian function has the maximum at 1613 cmminus1 andFWHM equal to 41 cmminus1 Four remaining Gaussian profilescan be divided into two pairs of narrow and broad functionsThe pair of broad profiles has the maxima at 1349 cmminus1 and1569 cmminus1 The corresponding FWHM values are equal to110 cmminus1 and 75 cmminus1 The narrow Gaussian functions arecentered at 1362 cmminus1 and 1582 cmminus1 The values of FWHMare equal to 47 cmminus1 and 31 cmminus1 respectively Parametersobtained from mathematical reconstruction of Nin-SiCcontact annealed at 1050∘C are summarized in Table 3

The focus of this paragraph is on carbon structurescreated due to thermal processes The first bands which canbe assigned to the vibrations related to carbon structureshave to be selected The following bands can be treated asbackground not directly related to carbon (i) Figure 13(a)bands centered at 1191 cmminus1 1587 cmminus1 and 1707 cmminus1 (ii)Figure 13(b) bands centered at 1476 cmminus1 and 1714 cmminus1 (iii)Figure 13(c) bands centered at 1194 cmminus1 1522 cmminus1 and1703 cmminus1 (iv) Figure 13(d) bands centered at 1170 cmminus11469 cmminus1 and 1666 cmminus1 (v) Figure 14 band centered at1474 cmminus1

In the case of Figures 13(a) 13(c) and 13(d) the firstGaussian profile (maximum placed below 1200 cmminus1) isrelatively narrow However the maximum of this function isplaced outside themeasured range of Raman shift Since onlya part of the fittedGaussian profile lies on experimental pointsin the measured spectrum the position of the function canbe inaccurateThe bands (i) 1587 cmminus1 from Figure 13(a) (ii)1476 cmminus1 from Figure 13(b) (iii) 1522 cmminus1 and 1703 cmminus1from Figure 13(c) (iv) 1469 cmminus1 and 1666 cmminus1 fromFigure 13(d) (v) 1474 cmminus1 fromFigure 14 have large FWHMvalues which exceeded 200 cmminus1 The band centered at1707 cmminus1 in Figure 13(a) has small contribution to thespectrum The band at 1714 cmminus1 in Figure 13(b) contributessignificantly However the signal-to-noise ratio is in this caseunfavorable so only the most distinct features of the spec-trum can be treated as reliable The above arguments suggestthat all the above-mentioned Gaussian profiles contributerather to the background although some of them can becorrelated with carbon structures in particular (i) bands1476 cmminus1 in Figure 13(b) and 1469 cmminus1 from Figure 13(d)can be correlated with vibrations of polyene [77] (ii) band1522 cmminus1 in Figure 13(c) can be correlated with amorphouscarbon [77] The other bands can be assigned to the productsrelated to silicon carbide decomposition

In the case of the reference sample five bands are relatedto the thermal decomposition of silicon carbide The bandcharacterized by the maximum placed at 1613 cmminus1 withFWHM equal to 41 cmminus1 can be assigned to Nickel-GraphiteIntercalation Compounds (Ni-GIC) [77] The formation ofmetal intercalation compounds during catalytic graphitiza-tion of 4H-SiC in the presence of nickel cobalt chromiumor other metals and at the temperature 800∘C or higher wasalready described in detail [77]

The other bands indicated in Figures 13 and 14 can beassigned to119863 and119866 vibrations reported for carbon structures[78] The most important features (i) maxima positions(ii) full width at half maximum (FWHM) and (iii) D-to-G intensity ratio (I(D)I(G)) of the bands obtained for theNi2Sin-SiC contacts annealed at 600 950 and 1050∘C are

summarized in Table 4 The bands obtained for the Ni2Sin-

SiC contact after annealing at 600∘C suggest a microcrys-talline character of the carbonThis is reflected in the positionof the 119866 band which is shifted higher than the standardposition reported for graphite [79] The band centered at1597 cmminus1 and FWHM equal to 91 cmminus1 is typical for Ramanspectra of microcrystalline carbon The one observed in thiscase is a combination of pure 119866 band and the band centeredat about 1620 cmminus1 and assigned to double C=C bonds andmarked in the literature as 1198631015840 [77] The bands are merged insuch a way that it is impossible to separate them Large valuesof FWHM obtained for both carbon bands equal to 61 cmminus1and 91 cmminus1 for119863 and119866 bands suggest large scattering of thestructural parameters of carbon species

In the case of the Ni2Sin-SiC contact annealed at 950∘C

maximum of 119863 band is shifted towards larger values ofRaman shift by 5 cmminus1 Ni

2Sin-SiC contact after annealing

at 600∘C The shift points to the increase of the thickness ofthe carbon layer with increasing annealing temperature from


Table 3 Properties of119863 and 119866 bands recorded for reference Ni119899-SiC contact

Sample D band G band119868(119863)119868(119866)

Maximum [cmminus1] FWHM [cmminus1] Maximum [cmminus1] FWHM [cmminus1]Ni broad 1349 110 1569 75 102Ni narrow 1362 47 1582 31 085

Table 4 Properties of D and G bands observed for the Ni2Si119899-SiC contacts annealed at 600 950 and 1050∘C


Maximum [cmminus1] FWHM [cmminus1] Maximum [cmminus1] FWHM [cmminus1]600∘C 1361 61 1597 91 078950∘C 1366 47 1584 51 0461050∘C 1360 48 1586 39 050

600 to 950∘C Such an effect was already observed for theovertone of119863 band ndash 2D [80]The FWHM of119863 and119866 bandsin the case of the Ni

2Sin-SiC contact annealed at 950∘C

are smaller than after annealing at 600∘C The reductionof FWHM values for both carbon bands suggests a morehomogeneous structure of carbon species in the Ni

2Sin-SiC

contact annealed at 950∘CThis is consistentwith the decreaseof I(D)I(G) intensity ratio obtained for samples Ni

2Sin-SiC

contact after annealing at 600∘C and the Ni2Sin-SiC contact

annealed at 950∘CThe values of D-to-G intensity ratio equalto 078 and 045 for the Ni

2Sin-SiC contact annealed at

600 and 950∘C respectively point to a higher graphitizationdegree in the case of second sampleThemaximumof119866 bandis equal to 1584 cmminus1 the standard value reported for graphite[78]

119863 and 119866 bands obtained for the sample with the Ni2Sin-

SiC contact annealed at 1050∘C have the maxima positionsequal to 1360 cmminus1 and 1586 cmminus1 respectively The bandsare shifted in opposite directions in comparison with bandsobserved for sample Ni


in particular 119863 band is shifted towards smaller values ofRaman shift by 6 cmminus1 and119866 band towards larger frequenciesby 2 cmminus1 This type of change was already reported forincrease of the content of ABA stacking order in comparisonwith ABC stacking order [81] ABC stacking order is pref-erentially formed during thermal decomposition of siliconcarbide especially at temperatures below 1000∘C [82] TheFWHM of 119863 band is in the case of the Ni

2Sin-SiC contact

annealed at 1050∘C almost the same as for the Ni2Sin-SiC

contact annealed at 950∘C (48 cmminus1 versus 47 cmminus1) Thesevalues point to similar distribution of structural parametersfor defected structures in both samples Significant reductionof FWHM for 119866 band in particular from 51 cmminus1 forthe Ni

2Sin-SiC contact annealed at 950∘C to 39 cmminus1 for

the Ni2Sin-SiC contact annealed at 1050∘C suggests more

homogeneous structure of carbon species in the Ni2Sin-SiC

contact annealed at 1050∘CThe parameters of the 119863 and 119866 bands obtained from

mathematical analysis of reference sample (Nin-SiC) arecollected in Table 3 The bands are divided into two groupsThe first one is composed of the 119863 and 119866 narrow bandsthe other group consists of 119863 and 119866 broad bands The pair

of narrow bands observed for the reference sample is similarto the 119863 and 119866 bands obtained for the Ni

2Sin-SiC contact

annealed at 1050∘C sample Small shift of the maxima posi-tions in particular (i) by 2 cmminus1 towards larger values ofRaman shift for119863 band (1362 cmminus1 versus 1360 cmminus1) and (ii)by 4 cmminus1 towards smaller values of Raman shift in the case of119866 band (1582 cmminus1 versus 1586 cmminus1) can be correlated withdifferent stacking order for both samples The shift of bothbands as described above suggests a larger contribution ofABC stacking order in reference sample than in the Ni

2Sin-

SiC contact annealed at 1050∘C [81] The value of FWHMfor 119863 narrow band is almost the same as in the case of119863 band observed for the Ni


1050∘C It points to almost the same distribution of structuralparameters for both samples Significantly smaller FWHMvalue of119866 band for reference sample (31 cmminus1 versus 39 cmminus1)suggests a more homogeneous structure of graphite speciesin Nin-SiC sample than in the Ni

2Sin-SiC contact annealed

at 1050∘C D-to-G intensity ratio is equal to 085 in the caseof narrow bands in reference sample This value is largerthan I(D)I(G) obtained for any sample from series Ni

2Sin-

SiC contact after annealing at 600∘C the Ni2Sin-SiC contact

annealed at 950∘C and the Ni2Sin-SiC contact annealed

at 1050∘C The value of D-to-G intensity ratio points tosmaller graphitization degree of Nin-SiC sample than eveninNiSiNiSin-SiC sample annealed at 600∘Cduring 15min

The other 119863 and 119866 bands form the pair of broad bandsBoth broad bands are shifted towards lower frequencies by13 cmminus1 in comparison with narrow bands The position of119863 and 119866 band as observed for the broad pair suggests thenanocrystalline graphitemixedwith sp3 phaseThe content ofsp3 phase should be about 10 [77 78] FWHM obtained for119863 band points to large distribution of structural parametersin defected structures It is almost twice as large as the valueobtained for theNi

2Sin-SiC contact after annealing at 600∘C

The value of FWHM obtained for the 119866 broad band is placedbetween the values for Ni


at 600∘C and the Ni2Sin-SiC contact annealed at 950∘C It

means that the homogeneity of graphite structure is betterthan for Ni

2Sin-SiC contact after annealing at 600∘C sample

but worse than for theNi2Sin-SiC contact annealed at 950∘C


Graphitization degree defined as I(D)I(G) is a commonlyused qualitative description of the carbon species The evo-lution of graphite structure can be divided into three stages[79] (i) graphite (g-C) rarr nanocrystalline graphite (nc-C)(ii) nc-C rarr amorphous carbon (a-C) (iii) a-C rarr tetrahe-dral a-C (ta-C) In the 1st stage the reduction of phononcorrelation length can be described by the following formulaI(D)I(G) sim 119871

119886

minus1 where 119871119886is called ldquoin-plane correlation

lengthrdquo and can be identified with the dimension of graphitegrain [78 79] The proportionality constant is dispersive forexample for wavelength equal to 5145 nm (green line of Ar+laser) this constant is equal to 44 A [78] The same value ofproportionality constant can be used for another importantAr+ laser line 488 nm [83] The formula is valid down to119871119886asymp (2 divide 3) nm [83] Since the graphite is not uniformly

nanocrystalline the grain dimension obtained from Ramanspectra should be taken as a mean value The maximumposition of 119866 band moves in this stage from about 1580 cmminus1to about 1600 cmminus1

In the 2nd stage the 119863 and 119866 bands evolve gradually tothe broad single band typical for a-C [79] The dimension ofthe grains is smaller than 2 nm The D-to-G intensity ratiois in this stage proportional to 119871

119886

2 and the proportionalityconstant for green line of Ar+ laser (5145 nm) is equal to00055 [83] In the 3rd stage I(D)I(G)asymp 0 [79]

Taking into account I(D)I(G) from Tables 3 and 4one can calculate the following grain sizes for all speciescontributing to Raman spectra (i) Ni

2Sin-SiC contact after

annealing at 600∘C (56 nm) at 950∘C (96 nm) and at1050∘C (88 nm) (ii) Nin-SiC contact after annealing at1050∘C (narrow bands 52 nm and broad bands 43 nm)Above-calculated grain dimensions show that carbon speciesobserved in samples investigated in this work can be dividedinto three groups (i) Ni

2Sin-SiC contact after annealing at

950∘C and Ni2Sin-SiC contact after annealing at 1050∘C

(ii) Ni2Sin-SiC contact after annealing at 600∘C and Nin-

SiC contact after annealing at 1050∘C (narrow bands) (iii)Nin-SiC contact after annealing at 1050∘C (broad bands)Furthermore it can be seen that Ni metallization resultsin creation of carbon grain with smaller size than NiSimetallization although the amount of carbon appearing dueto silicon carbide decomposition is significantly larger

Thus the deposition of NiSiNiSi sequence of layerscombined with annealing at 600∘C results in creation of asilicide layer with negligible decomposition of SiC [26 38]The intensities of119863 and119866 bands increase with the increase ofthe annealing temperature This is clearly visible in Figure 13Annealing at higher temperature after creation of silicidelayer slows down the process of thermal decompositionThe intensities of 119863 and 119866 bands in the case of Ni

2Sin-

SiC contacts are significantly smaller than the intensities ofthese bands obtained for the reference sample (Nin-SiC)In the case of Ni

2Sin-SiC contact the initial structure built

from sequence of silicon and nickel layers results in the fastformation of a silicide In the case of the Nin-SiC contactcatalyzed by Ni decomposition the decomposition of largeramount of SiC is observed This is confirmed by results fromRaman measurements and other techniques Raman spectra

recorded for the reference sample point to larger amountof carbon in comparison with samples Ni

2Sin-SiC On the

other hand the quality of the carbon formed in the sampleNi2Sin-SiC (1050∘C) ismuch higher than in reference sample

as proven by the graphitization degree reflected in I(D)I(G)ratio and by scattering of structural parameters visible inFWHM of the bands

The other problem is the location of carbon species Inthe case of Ni

2Sin-SiC contacts the rate of decomposition

is small Experimental techniques like XRD or HRTEM didnot detect traces of carbon either on the SiCsilicide interfaceor in the silicide layer Moreover the intensities of Ramanspectra recorded for these contacts are very low and theconcentration of carbon species may be not detectable byXRD The situation looks different for the Nin-SiC contactA mathematical analysis of the Raman spectra points to twodifferent types of carbon Each type is characterized by thepair of 119863 and 119866 bands The pair of broad bands shouldcharacterize the carbon species appearing on SiCsilicideinterface Large values of FWHM suggest large scatteringof structural parameters This situation is typical for carbonformed during thermal decomposition of silicon carbideThe other pair of bands called narrow corresponds to thesecond type of carbon The FWHM values suggest scatteringof structural parameters comparable with the Ni

2Sin-SiC

(1050∘C) sample D-to-G ratio points to lower graphitizationdegree in comparison with Ni

2Sin-SiC (1050∘C) sample

although the annealing of both samples was done at the sametemperature

Lower graphitization degree together with higher decom-position ratio in the case of reference sample results fromdifferent metallization In the case of the NiSi sequence oflayers Ni is mixed with Si and silicides can be created almostwithout decomposition of SiC substrate Metallization withsingle Ni layers requires SiC decomposition in order to getthe Si necessary to form the silicide layer Decompositionof a large volume of the SiC substrate results on the otherhand in a larger carbon presence This carbon diffuses fromthe interface to the silicide surface where the graphite layerwith relatively high graphitization degree is createdThis is inagreement with the data reported in the literature [84] whichsuggest that the thermal treatment above 1000∘C acceleratesdecomposition of silicon carbide and diffusion of carbonfrom interface area Creation of graphite layer on the freesilicide surface in the case of reference sample is supportedby data presented in this work and obtained from otherexperimental techniques For example investigation withhigh-resolution TEM did not detect the traces of carbonstructures at the interface between silicide layer and SiCsubstrate

The other problem is the location of carbon speciesresponsible for the ldquobroadrdquo pairs of119863 and 119866 bands observedfor the sample with NiSiC metallization XRD and RBS pro-files discussed in this work suggest a nonuniformdistributionof carbon structures in metallization layer Relatively largevalues of FWHM for this pair of bands suggest scattering ofthe structural parameters of the species responsible for thepresence of pair of ldquobroadrdquo D and 119866 bands


Table 5 Electrical properties of AuNi2Sin-SiC and AuTa

35Si15N50Ni2Sin-SiC ohmic contacts versus heat treatments

Heat treatments AuNi2Sin-SiC AuTa

35Si15N50Ni2Sin-SiC

119903119888(times10minus4Ω cm2) 119877sh (Ωsq) 119903

119888(times10minus4Ω cm2) 119877sh (Ωsq)

As-deposited sim4 029 sim4 029800∘CAr3min sim45 026 sim4 022400∘Cair150 h Nonohmic 068 sim45 017

46 Thermal Stability of Ni2Si-Based Ohmic Contacts to n-

Type 4H-SiC Fabrication of low-resistive ohmic contacts tosilicon carbide (SiC) is not sufficient for application to SiC-based devices For usage of those SiC-based devices in harshenvironments investigation of their reliability for examplethermal stability is needed [85ndash92] In order to investigatethe thermal stability of Ni

2Si-based ohmic contacts to n-type

4H-SiC the influence of heat treatment conditions such aslong-term aging in air at 400∘C and rapid thermal annealing(RTA) in a neutral atmosphere (Ar) at 800∘C on the reliabilityof Ni2Sin-SiC ohmic contacts with a top Au mounting layer

was studied A part of the prepared structures had a Ta-Si-Ndiffusion barrier introduced between the Ni

2Si and Au layers

Gold has been chosen as the overlayer for interconnectionor bonding metallization as it is a highly conductive metalcompatible with the standard semiconductor technologyThe nanocomposite Ta-Si-N layers selected for the diffusionbarriers were shown to have excellent diffusion-blockingproperties in contacts to Si [92] GaAs [93 94] andGaN [95]

The electrical properties before and after heat treatmentsof the Au (150 nm)Ni

2Sin-SiC and Au (150 nm)Ta

35Si15N50

(100 nm)Ni2Sin-SiC ohmic contact stacks are summarized

in Figure 15 and Table 5 The specific contact resistance 119903119888sim

4 times 10minus4Ω cm2 for the as-deposited AuNi

2Sin-SiC contacts

remains unchanged after RTA at 800∘C (Ar 3min) howeverthe I-V characteristics start to exhibit nonohmic behaviorafter aging at 400∘C (air 150 h) For the AuTaSiNNi

2Sin-

SiC contacts the 119903119888sim 4times10

minus4Ω cm2 remains unchanged after

RTA at 800∘C (Ar 3min) as well as after aging at 400∘C (air150 h) The initial sheet resistance (119877sh sim 029Ωsq) for bothas-deposited contacts corresponds to the resistivity of highlyconductive 150 nm thick Au overlayer (120588 sim 44 120583Ω cm) Thisvalue exceeds the resistivity of bulk Au (120588 sim 25 120583Ω cm [96])due to the scattering of electrons by the film grain boundariesFor the AuNi

2Sin-SiC contacts 119877sh decreases by sim10 and

increases by sim230 after RTA (800∘C Ar) and aging (400∘Cair) respectively On the contrary for the AuTaSiNNi

2Sin-

SiC contacts 119877sh decreases by sim25 and sim40 after RTA(800∘CAr) and aging (400∘C air) respectivelyThe observeddecrease in 119877sh can be related to recrystallization of the Aulayers with a subsequent reduction of grain boundary densityOne of the reasons for such an explanation is the fact that119877sh sim 02Ωsq for the treated contacts corresponds to theresistivity 120588 sim 3 120583Ω cm which is very close to the value forbulk Au On the other hand the increase of 119903

119888and 119877sh can be

attributed to the diffusion processes in metallization systemsunder thermal stress For further studies of these contactsXRD RBS and SEM techniques were applied

XRD spectra of the AuNi2Sin-SiC and AuTaSiNNi

2Si

n-SiC contact stacks before and after heat treatments areshown in Figure 16 The XRD spectra of the as-depositedstacks are similar in both cases Apart from the (0004) peak ofthe single crystal 4H-SiC only peaks from polycrystalline Au(111) and orthorhombic 120575-Ni

2Si (013) are observed showing

that the Au and 120575-Ni2Si grains are textured After annealing

at 800∘C (Ar 3min) for both stacks only a small shift ofthe Au and 120575-Ni

2Si peaks to higher Bragg angles is detected

due to the recrystallization of Au grains and strain relaxationat the Aucontact interface Similar changes are observed intheXRD spectra (Figure 16(b)) for theAuTaSiNNi

2Sin-SiC

stacks after aging at 400∘C (air 150 h) However when thesame aging conditions were applied to the AuNi

2Sin-SiC

stacks a strong decrease in the intensity of the (013) 120575-Ni2Si

peak splitting of the (111) Au peak and an appearance of newpeaks were observed (Figure 14(a))This can be interpreted asa decomposition of Ni

2Si leading to the formation of pure Ni

and Ni31Si12phases as well as a Au

119909(NiSi)

1minusx solid solutionRBS profiles of the AuNi

2Sin-SiC contact stacks are

shown in Figure 17(a) The only difference between theprofiles measured for the as-deposited and RTP-annealed(800∘C Ar 3min) samples is the appearance of a small Nisurface signal (sim15MeV) Apart from this feature the profilesoverlap which indicates no redistribution of the elementsafter annealing However subsequent aging of the stacks at400∘C (air 150 h) results in a considerable change of theRBS profiles Significant changes of the signal from Au thedisappearance of the signal from Ni

2Si and the appearance

of Ni (sim15MeV) and O (sim07MeV) signals are observedThis indicates a strong interaction at both the AuNi

2Si and

Ni2Sin-SiC interfaces after aging Simulation shows an in-

diffusion of Au atoms into the contact out-diffusion of Niand Si atoms to the surface and oxygen penetration intothe contact This correlates well with the strong degradationof the electrical properties of the contacts observed (seeTable 5) On the other hand the overlap of the RBS profilesfor the as-deposited annealed at 800∘C (Ar 3min) and agedat 400∘C (air 150 h) AuTaSiNNi

2Sin-SiC contact stacks

shown in Figure 15(b) indicates that the Ta-Si-N diffusionbarrier introduced between the Au overlayer and theNi

2Sin-

SiC ohmic contact successfully blocks any interdiffusion andretains abrupt interfaces with the neighbouring layers

Figure 18 shows SEM images of the AuNi2Sin-SiC and

AuTa35Si15N50Ni2Sin-SiC contact stacks before and after

heat treatments The surface morphology of the as-depositedcontacts is shown in Figures 18(a) and 18(c) and appearsrelatively smooth Annealing of the AuNi

2Sin-SiC stacks

at 800∘C (Ar 3min) leads to a modification of the gold


Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC

As-deposited700∘CAr3min800∘CAr3min

(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC

As-deposited400∘Cair50h400∘Cair150h

(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

As-deposited400∘Cair50h

AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)

Figure 15 Current-voltage characteristics for the AuNi2Sin-SiC (a b) and AuTa

35Si15N50Ni2Sin-SiC (c d) ohmic contacts versus heat

treatments

surface due to a recrystallization leading to an increaseof Au grain size and subsequent pore formation in theAu layer (Figure 16(a)) The pores are responsible for theappearance of the Ni surface signal in the RBS spectrumof this contact stack (Figure 17(a)) Similar surface changesare detected for the AuTaSiNNi

2Sin-SiC contact stack after

annealing at 800∘C (Ar 3min) but a smaller number ofpores in the Au layer are observed (Figure 18(c)) For theAuNi

2Sin-SiC contacts aged at 400∘C (air 150 h) granular

areas and craters appear in the Au layer both indicatingstrong morphology degradation (Figure 18(b)) The depth ofthe craters (ge295 nm) exceeds the thickness (sim250 nm) of theAuNi

2Si metallization and their average surface density is

about 2000mmminus2 Thus we can assume that oxygen diffuses

into the contact preferentially via the craters created in themetallization Aging the AuTa

35Si15N50Ni2Sin-SiC contact

stacks at 400∘C (air 150 h) results only in small modificationsof the surface morphology due to the recrystallization of Augrains the contact surface still is relatively smooth surface

Thus for the AuNi2Sin-SiC contacts without the Ta-

Si-N diffusion barrier the degradation of the electricalcharacteristics correlates well with phase transformationdepth redistribution of elements and oxygen penetrationIt has to be noted that it was previously reported that thedegradation of electrical properties in air comes mainlyfrom the diffusion of oxygen into the contacts [97 98]However apart from the oxidation of the contacts oxygen


XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12

AuNi2Sin-SiCAs-deposited800∘CAr3min400∘Cair150h

Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

As-deposited800∘CAr3min400∘Cair150h

Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)

Figure 16 XRD spectra of the AuNi2Sin-SiC (a) and AuTa

35Si15N50Ni2Sin-SiC (b) ohmic contacts before and after heat treatments


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)

Figure 17 RBS spectra of the AuNi2Sin-SiC (a) and AuTa

35Si15N50Ni2Sin-SiC (b) ohmic contacts before and after heat treatments By an

arrow are marked the surface energies of the respective elements

plays the role of a catalyst which enhances interdiffusionandor reaction in metalSiC contacts Investigations of theAuTaSiNNi

2Sin-SiC contacts show their superior thermal

stability This can be concluded from the abrupt contactinterfaces no redistribution of the elements over the depthas well as from the preserved smooth surface and the phasecomposition after heat treatments

We conclude that the thermal stability of Ni2Sin-SiC

ohmic contacts withAu overlayer dependsmainly on the heattreatment conditions as well as the presence of a diffusionbarrier We observed that degradation of the ohmic contactsbecomes stronger after long-time aging in air at relatively lowtemperature (400∘C) than after RTA at 800∘C in a neutral gas(Ar) An optimized Ta

35Si15N50diffusion barrier introduced


As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h

Figure 18 SEM micrographs of the AuNi2Sin-SiC (a and b) and AuTa

35Si15N50Ni2Sin-SiC (c and d) ohmic contacts (a c) as-deposited

and after annealing in Ar at 800∘C (3min) (b d) after aging in air at 400∘C (150 h) [85ndash88] The yellow squares show the SEM micrographswith higher resolution for the contacts after heat treatments

between the Ni2Sin-SiC ohmic contact and Au overlayer

prevents the interdiffusion of metals in the contact region aswell as the penetration of oxygen during long-time aging inair

5 Discussion and Conclusions

The common processes in the reaction of metals with SiCcould be as follows formation of silicides and free carbonor formation of carbides and silicides [99] The propertiesof the contact materials affect the final reaction productsConcerning the Ni-based metallization the Ni-silicides andfree carbon are formed during the reaction of pure Ni withSiC Both carbides and silicides are formed by adding astrong carbide former metal (Ti Mo etc) to the Ni-basedmetallization scheme [13 44 91 100 101]

Many technological parameters have strong influenceon Ni-based metal reaction with SiC All these parameterscan affect both the structural and electrical properties ofthe contacts Nevertheless some common features becomeevident (i) the formation of the Ni

2Si phase either by an

interaction between Ni and SiC by a solid state reactionbetween Ni and Si single layers or by a deposition ofNi2Si layers on SiC creates a relatively high quality Schottky

contact to n-SiC up to annealing le700∘C (ii) annealingat high temperature (gt900∘C) leads to the transition fromrectifying to ohmic contact for the same metallization BothNi-based Schottky and ohmic contacts annealed at differenttemperature are used for SiC-based semiconductor devices

[102ndash105] There are many studies that show a consensus ofNi2Sin-SiC Schottky contacts which have the barrier height

120593119861sim 16 eV [10ndash12 16ndash18 29ndash32] However there is still little

consensus regarding why the barrier height decreases andNi2Sin-SiC contacts become ohmic after annealing at tem-

perature or above 900∘C How does the Ni2Si phase create

both Schottky and ohmic contacts to n-SiCA steep reduction of specific contact resistances and

decrease in 120593119861at temperatures over 900∘C for Ni-based

ohmic contact to n-SiC was observed by Tanimoto et al[106] Using cross-sectional TEM-EDS (energy dispersive X-ray spectroscopy) analysis has made such conclusions (i)the surface of substrates annealed at 1000∘C was not coveredwith Ni

2Si but with a thin layer of NiSi (ii) the formation of

the NiSiSiC system contributes to the significant reductionin contact resistance On the other hand in the series ofpapers particular attention was paid to the role of carbonplaced on the silicideSiC interface [77 107 108] It wasshown that carbon on this interface can play catalytic rolein the formation of ohmic contact The transition fromSchottky to ohmic behavior was achieved after annealing in800∘CThis temperature is significantly lower in comparisonwith standard values reported for samples without additionalcarbon layer deposited on the interface during the manufac-turing process Ni-silicides appear generally at temperaturesbetween 400 and 600∘C [50 109] The hypothesis that thegraphite layer placed on the interface is responsible for theohmic character of contact was supported by ohmic characterof graphite layer placed on silicon carbide [51] However as


was shown the carbon atoms can be present on the interfaceat the temperatures in which ohmic character of the contactis not observed On the other side the diffusion of carbonatoms towards the free silicide surface was observed at highertemperatures than the temperature necessary for creation of asilicide layer [54]The other postulated mechanism responsi-ble for ohmic character of the contact is related to structuralchanges of the SiC substrate in close vicinity of silicideSiCinterface [110]These changes are caused by creation of emptyplaces so-called vacancies which lower the Schottky barrier[42 71 111] The mechanism which is suspected for creationof these vacancies is diffusion of carbon atoms towards freesilicide surface [71 111] Moreover using DLTS in an effortto detect a high concentration of carbon vacancies for 950∘Cannealed contacts suggests that this model is correct [31 53]All available data does not allow authors to point to onesimple mechanism which can describe the contribution ofcarbon atoms to creation of ohmic contactsThe investigationof the samples with additional carbon layer deposited onthe interface suggests only a catalytic role of this elementin creation of ohmic contacts Moreover the data obtainedin this work do not confirm the presence of carbon atomson the Ni

2SiSiC interface This suggests that contribution of

carbon to ohmic contact creation may be very complex andthe exact mechanism may be modified by parameters of thewhole manufacturing process

Thus based on our reported results we may concludethat only 120575-Ni

2Si grains play a key role in determining

electrical transport properties at the contactSiC interfaceIt should be noted that the creation of Ni

2Si phase on n-

SiC is not sufficient for the formation of an ohmic contactOnly the recrystallization of Ni

2Si phase after annealing

at high temperature (gt900∘C) leads to the transition fromrectifying to ohmic contact by lowering barrier height fromsim16 eV to sim045 eV We suppose that only 120575-Ni

2Si grains

that are in the orientation-relationship with (0001)SiC(013)120575-Ni2Si after high-temperature annealing are area with low

barrier height [71] Indeed from Ni-silicides only 120575-Ni2Si is

thermodynamically stable with SiC which agrees well withthe Ni-Si-C ternary phase diagram (tie lines connect 120575-Ni

2Si

with SiC and C) [112]Vivona et al [113] demonstrated the thermal stability of

the Ni2Sin-SiC ohmic contact after long-term (up to 95 h)

thermal cycling in N2atmosphere at different temperatures

(in the range 200ndash400∘C)The thermal stability of the currenttransport mechanisms the specific contact resistance andbarrier height (sim045 eV) were observed At the same timeannealing in air [85ndash88] leads to the catastrophic degradationof omicity of the Ni

2Sin-SiC contact Thus the diffusion

barriers with free diffusion path microstructure are keyelements to improve thermal stability of metal-SiC ohmiccontacts for high-temperature electronics

Finally summarizing this paper we conclude that man-ufacturing of high quality ohmic contacts requires opti-mization of ldquomultiparametric functionrdquoThe parameters thatshould be included are (i) quality of silicon carbide (ii)surface before treatment (iii) metallization scheme (typeof metals thicknesses sequence of deposition and diffu-sion barrier) (iv) contact passivation against corrosion and

(v) annealing type (sequence of temperature and applicationtime atmosphere of thermal process and cooling and heatingratios)

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

Acknowledgments

The authors wish to thank Dr R Minikayev (Institute ofPhysicsWarsaw Poland) Dr O Lytvyn (V Lashkaryov Insti-tute of Semiconductor Physics Kyiv Ukraine) and M Latek(Institute of Electron Technology Warsaw Poland)Dr OKolomys (V Lashkaryov Institute of Semiconductor PhysicsKyiv Ukraine) for XRD AFM and Raman measurementsrespectively

References

[1] httpwwwiofferuSVANSM[2] T Kimoto and J A Cooper Fundamentals of Silicon Carbide

Technology Growth Characterization Devices and Applica-tions John Wiley amp Sons Singapore 2014

[3] P Friedrichs T Kimoto L Ley and G Pensl Silicon CarbideGrowth Defects and Novel Applications vol 1 Wiley-VCHVerlag GmbH amp Co KGaA Weinheim Germany 2010

[4] L M Porter and R F Davis ldquoA critical review of ohmic andrectifying contacts for silicon carbiderdquo Materials Science andEngineering B vol 34 no 2-3 pp 83ndash105 1995

[5] J Crofton L M Porter and J R Williams ldquoThe physics ofOhmic contacts to SiCrdquoPhysica Status Solidi (B) Basic Researchvol 202 no 1 pp 581ndash603 1997

[6] F Roccaforte F La Via and V Raineri ldquoOhmic contacts to SiCrdquoInternational Journal of High Speed Electronics and Systems vol15 no 4 pp 781ndash820 2005

[7] W R Harrell J Zhang and K F Poole ldquoAluminum Schottkycontacts to n-type 4H-SiCrdquo Journal of Electronic Materials vol31 no 10 pp 1090ndash1095 2002

[8] U Zimmermann A Hallen and B Breitholtz ldquoCurrent volt-age characteristics of high-voltage 4H silicon carbide diodesrdquoMaterials Science Forum vol 338ndash342 pp 1323ndash1326 2000

[9] K P Schoen J M Woodall J A Cooper and M R MellochldquoDesign considerations and experimental analysis of high-voltage SiC Schottky barrier rectifiersrdquo IEEE Transactions onElectron Devices vol 45 no 7 pp 1595ndash1604 1998

[10] A Itoh and HMatsunami ldquoAnalysis of schottky barrier heightsof metalSiC contacts and its possible application to high-voltage rectifying devicesrdquo Physica Status Solidi (A) vol 162 no1 pp 389ndash408 1997

[11] D Perrone M Naretto S Ferrero L Scaltrito and C F Pirrildquo4H-SiC schottky barrier diodes using Mo- Ti- and Ni-basedcontactsrdquo Materials Science Forum vol 615ndash617 pp 647ndash6502009

[12] F La Via F Roccaforte A Makhtari V Raineri P Musumeciand L Calcagno ldquoStructural and electrical characterisationof titanium and nickel silicide contacts on silicon carbiderdquoMicroelectronic Engineering vol 60 no 1-2 pp 269ndash282 2002


[13] P A Ivanov A S Potapov and T P Samsonova ldquoAnalysis offorward current-voltage characteristics of non-ideal Ti

4H-SiC

Schottky barriersrdquo Materials Science Forum vol 615ndash617 pp431ndash434 2009

[14] T Hatayama K Kawahito H Kijima Y Uraoka and TFuyuki ldquoElectrical properties and interface reaction of annealedCu4H-SiC schottky rectifiersrdquo Materials Science Forum vol389ndash393 pp 925ndash928 2002

[15] C Koliakoudakis J Dontas S Karakalos et al ldquoFabricationand characterization of Cr-based SchottkyDiode on n-type 4H-SiCrdquoMaterials Science Forum vol 615ndash617 pp 651ndash654 2009

[16] A Kestle S P Wilks P R Dunstan M Pritchard andP A Mawby ldquoImproved NiSiC Schottky diode formationrdquoElectronics Letters vol 36 no 3 pp 267ndash268 2000

[17] V Saxena J-N Su and A J Steckl ldquoHigh-voltage Ni- andPt-SiC Schottky diodes utilizing metal field plate terminationrdquoIEEE Transactions on Electron Devices vol 46 no 3 pp 456ndash464 1999

[18] I Nikitina K Vassilevski A Horsfall et al ldquoPhase inhomo-geneity and electrical characteristics of nickel silicide Schottkycontacts formed on 4H-SiCrdquoMaterials Science Forum vol 615ndash17 pp 577ndash580 2009

[19] W Jung and M Guziewicz ldquoSchottky diode parameters extrac-tion using Lambert W functionrdquo Materials Science and Engi-neering B vol 165 no 1-2 pp 57ndash59 2009

[20] H-J Im B Kaczer J P Pelz andW J Choyke ldquoBallistic electronemission microscopy study of Schottky contacts on 6H- and4H-SiCrdquoApplied Physics Letters vol 72 no 7 pp 839ndash841 1998

[21] H-J Im B Kaczer J P Pelz J-M Chen et al ldquoNanometer-scale investigation of Schottky contacts and conduction bandstructure on 4H- 6H- and 15R-SiC using ballistic electronemission microscopyrdquo Materials Science Forum vol 264ndash268pp 813ndash816 1998

[22] O Shigiltchoff T Kimoto D Hoodgood et al ldquoSchottkybarriers for Pt Mo and Ti on 6H and 4H SiC (0001) (0001)(1100) and (1210) faces measured by I-V C-V and internalphotoemissionrdquo in Proceedings of the Technical Digest of Inter-national Conference on SiC and Related Materials We-B-23 p291 Tsukuba Japan 2001

[23] A F Hamida Z Ouennoughi A Sellai R Weiss and HRyssel ldquoBarrier inhomogeneities of tungsten Schottky diodeson 4H-SiCrdquo Semiconductor Science and Technology vol 23 no4 Article ID 045005 2008

[24] C F Zhe Silicon Carbide Materials Processing amp DevicesTaylor amp Francis New York NY USA 2004

[25] M Wiets M Weinelt and T Fauster ldquoElectronic structureof SiC(0001) surfaces studied by two-photon photoemissionrdquoPhysical Review B vol 68 no 12 Article ID 125321 2003

[26] A V Kuchuk V P KladkoMGuziewicz et al ldquoFabrication andcharacterization of nickel silicide ohmic contacts to n-type 4Hsilicon carbiderdquo Journal of Physics Conference Series vol 100part 4 Article ID 042003 2008

[27] J Crofton P G McMullin J R Williams and M J BozackldquoHighminustemperature ohmic contact to nminustype 6HminusSiC usingnickelrdquo Journal of Applied Physics vol 77 no 3 pp 1317ndash13191995

[28] M G Rastegaeva A N Andreev A A Petrov A I BabaninMA Yagovkina and I P Nikitina ldquoThe influence of temperaturetreatment on the formation of Ni-based Schottky diodes andohmic contacts to n-6H-SiCrdquoMaterials Science and EngineeringB vol 46 no 1ndash3 pp 254ndash258 1997

[29] S P Avdeev O A Agueev R V Konakova et al ldquoEffect ofpulse thermal treatments on the Ni(Ti)n-21R(6H)-SiC contactparametersrdquo Semiconductor Physics Quantum Electronics ampOptoelectronics vol 7 no 3 pp 272ndash278 2004

[30] T Marinova V Krastev C Hallin R Yakimova and E JanzenldquoInterface chemistry and electric characterisation of nickelmetallisation on 6H-SiCrdquo Applied Surface Science vol 99 no2 pp 119ndash125 1996

[31] F La Via F Roccaforte V Raineri et al ldquoSchottky-ohmictransition in nickel silicideSiC-4H system is it really a solvedproblemrdquoMicroelectronic Engineering vol 70 no 2ndash4 pp 519ndash523 2003

[32] F Roccaforte F La Via V Raineri L Calcagno and P Musu-meci ldquoImprovement of high temperature stability of nickelcontacts on n-type 6H-SiCrdquo Applied Surface Science vol 184no 1ndash4 pp 295ndash298 2001

[33] T Marinova A Kakanakova-Georgieva V Krastev et alldquoNickel based ohmic contacts on SiCrdquo Materials Science andEngineering B vol 46 no 1ndash3 pp 223ndash226 1997

[34] A Kakanakova-Georgieva T Marinova O Noblanc C Arn-odo S Cassette and C Brylinski ldquoCharacterization of ohmicand Schottky contacts on SiCrdquo Thin Solid Films vol 343-344no 1-2 pp 637ndash641 1999

[35] S J Yang C K Kim I H Noh S W Jang K H Jung and NI Cho ldquoStudy of Co- and Ni-based ohmic contacts to n-type4H-SiCrdquo Diamond and Related Materials vol 13 no 4ndash8 pp1149ndash1153 2004

[36] T Nakamura and M Satoh ldquoSchottky barrier height of a newohmic contact NiSi

2to n-type 6H-SiCrdquo Solid-State Electronics

vol 46 no 12 pp 2063ndash2067 2002[37] C Deeb and A H Heuer ldquoA low-temperature route to thermo-

dynamically stable ohmic contacts to n-type 6H-SiCrdquo AppliedPhysics Letters vol 84 no 7 p 1117 2004

[38] A V Kuchuk V P Kladko A Piotrowska R Ratajczak andR Jakiela ldquoOn the formation of Ni-based ohmic contacts to n-type 4H-SiCrdquo Materials Science Forum vol 615ndash617 pp 573ndash576 2009

[39] E Kurimoto H Harima T Toda M Sawada M Iwami andS Nakashima ldquoRaman study on the NiSiC interface reactionrdquoJournal of Applied Physics vol 91 no 12 pp 10215ndash10217 2002

[40] T Seyller K V Emtsev K Gao et al ldquoStructural and electronicproperties of graphite layers grown on SiC(0 0 0 1)rdquo SurfaceScience vol 600 no 18 pp 3906ndash3911 2006

[41] L Calcagno A Ruggiero F Roccaforte and F La Via ldquoEffectsof annealing temperature on the degree of inhomogeneity ofnickel-silicideSiC Schottky barrierrdquo Journal of Applied Physicsvol 98 no 2 Article ID 023713 2005

[42] I PNikitina KVVassilevski NGWright A BHorsfall AGOrsquoNeill andCM Johnson ldquoFormation and role of graphite andnickel silicide in nickel based ohmic contacts to n-type siliconcarbiderdquo Journal of Applied Physics vol 97 no 8 Article ID083709 2005

[43] W Lu W C Mitchel G R Landis T R Crenshaw and W ECollins ldquoCatalytic graphitization and Ohmic contact formationon 4H-SiCrdquo Journal of Applied Physics vol 93 no 9 pp 5397ndash5403 2003

[44] M H Ervin K A Jones M A Derenge et al ldquoIn situ SEMobservations and electrical measurements during the annealingof SiNi contacts to SiCrdquo in Proceedings of theMaterials ResearchSociety Symposium vol 764 ofMRS Proceeding 2003


[45] B Barda P Machac M Hubickova and J Nalik ldquoComparisonof NiTi and Ni ohmic contacts on n-type 6HndashSiCrdquo Journal ofMaterials Science Materials in Electronics vol 19 no 11 pp1039ndash1044 2008

[46] G V Samsonov and I M Vinitdky Refractory CompoundsMetallurgija Moscow Russia 1976 (Russian)

[47] L J Chen Silicide Technology for IntegratedCircuits (Processing)Institution of Electrical Engineers 2004

[48] N Biswas J Gurganus and V Misra ldquoWork function tuningof nickel silicide by co-sputtering nickel and siliconrdquo AppliedPhysics Letters vol 87 no 17 Article ID 171908 2005

[49] A Bachli M-A Nicolet L Baud C Jaussaud and R MadarldquoNickel film on (001) SiC thermally induced reactionsrdquo Mate-rials Science and Engineering B vol 56 no 1 pp 11ndash23 1998

[50] Z Zhang J Teng W X Yuan F F Zhang and G H ChenldquoKinetic study of interfacial solid state reactions in the Ni4HndashSiC contactrdquo Applied Surface Science vol 255 no 15 pp 6939ndash6944 2009

[51] W Lu W C Mitchel C A Thornton G R Landis andW Eugene Collins ldquoCarbon structural transitions and ohmiccontacts on 4HndashSiCrdquo Journal of Electronic Materials vol 32 no5 pp 426ndash431 2003

[52] S Y Han and J-L Lee ldquoEffect of interfacial reactions onelectrical properties of Ni contacts on lightly doped n-type 4HndashSiCrdquo Journal of the Electrochemical Society vol 149 no 3 ppG189ndashG193 2002

[53] L Calcagno E Zanetti F La Via et al ldquoSchottky-ohmictransition in nickel sllicideSiC system is it really a solvedproblemrdquo Materials Science Forum vol 433ndash436 pp 721ndash7242003

[54] R Colby M L Bolen M A Capano and E A Stach ldquoAmor-phous interface layer in thin graphite films grown on the carbonface of SiCrdquo Applied Physics Letters vol 99 no 10 Article ID101904 2011

[55] A Hahnel V Ischenko and J Woltersdorf ldquoOriented growthof silicide and carbon in SiC-based sandwich structures withnickelrdquo Materials Chemistry and Physics vol 110 no 2-3 pp303ndash310 2008

[56] A Hahnel E Pippel V Ischenko and J Woltersdorf ldquoNanos-tructuring in NiSiC reaction layers investigated by imagingof atomic columns and DFT calculationsrdquoMaterials Chemistryand Physics vol 114 no 2-3 pp 802ndash808 2009

[57] A A Woodworth and C D Stinespring ldquoSurface chemistry ofNi induced graphite formation on the 6H-SiC (0 0 0 1) surfaceand its implications for graphene synthesisrdquoCarbon vol 48 no7 pp 1999ndash2003 2010

[58] J C Burton L Sun F H Long Z C Feng and I TFerguson ldquoFirst- and second-order Raman scattering fromsemi-insulating 4H-SiCrdquoPhysical Review BmdashCondensedMatterand Materials Physics vol 59 no 11 pp 7282ndash7284 1999

[59] P Borowicz A Kuchuk Z Adamus et al ldquoStructure of carboniclayer in ohmic contacts comparison of silicon carbidecarbonand carbonsilicide interfacesrdquo ISRN Physical Chemistry vol2013 Article ID 487485 11 pages 2013

[60] M Mayer ldquoSIMNRA a simulation program for the analysis ofNRA RBS and ERDArdquo in Proceedings of the 15th InternationalConference on the Application of Accelerators in Research andIndustry J L Duggan and I L Morgan Eds vol 475 p 5411999 AIP Conference Proceedings

[61] B Pecz G Radnoczi S Cassette C Brylinski C Arnodo andONoblanc ldquoTEM study ofNi andNi

2Si ohmic contacts to SiCrdquo

Diamond and Related Materials vol 6 no 10 pp 1428ndash14311997

[62] M W Cole P C Joshi and M Ervin ldquoFabrication and charac-terization of pulse laser deposited Ni

2Si Ohmic contacts on n-

SiC for high power and high temperature device applicationsrdquoJournal of Applied Physics vol 89 no 8 pp 4413ndash4416 2001

[63] I Nikitina K Vassilevski A Horsfall et al ldquoPhase compositionand electrical characteristics of nickel silicide Schottky contactsformed on 4HndashSiCrdquo Semiconductor Science and Technology vol24 no 5 Article ID 055006 2009

[64] G Hui Z Yi-Men Q Da-Yong S Lei and Z Yu-Ming ldquoThefabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbiderdquo Chinese Physics vol 16 no 6 pp 1753ndash17562007

[65] P Colombi E Bontempi U M Meotto et al ldquoAmorphous NindashZr layer applied for microstructure improvement of Ni-basedohmic contacts to SiCrdquoMaterials Science and Engineering B vol114-115 pp 236ndash240 2004

[66] A V Kuchuk K Gołaszewska V P Kladko et al ldquoTheformation mechanism of Ni-based ohmic contacts to 4H-n-SiCrdquoMaterials Science Forum vol 717ndash720 pp 833ndash836 2012

[67] M Wzorek A Czerwinski A Kuchuk J Ratajczak APiotrowska and J Katcki ldquoTEM characterisation of suicidephase formation in Ni-based ohmic contacts to 4H n-SiCrdquoMaterials Transactions vol 52 no 3 pp 315ndash318 2011

[68] M Wzorek A Czerwinski A Kuchuk J Ratajczak APiotrowska and J Kątcki ldquoNi-based ohmic contacts to siliconcarbide examined by electron microscopyrdquo Solid State Phenom-ena vol 186 pp 82ndash85 2012

[69] M Wzorek A Czerwinski M A Borysiewicz et al ldquoAmor-phous NindashZr layer applied for microstructure improvementof Ni-based ohmic contacts to SiCrdquo Materials Science andEngineering B vol 199 pp 42ndash47 2015

[70] M Wzorek A Czerwinski J Ratajczak et al ldquoMicrostructurecharacterization of SiNi contact layers on n-type 4H-SiC byTEM and XEDSrdquo Materials Science Forum vol 778ndash780 pp697ndash701 2014

[71] S Y Man K H Kim J K Kim et al ldquoOhmic contact formationmechanism of Ni on n-type 4HndashSiCrdquo Applied Physics Lettersvol 79 no 12 pp 1816ndash1818 2001

[72] A Y C Yu ldquoElectron tunneling and contact resistance ofmetal-silicon contact barriersrdquo Solid-State Electronics vol 13 no 2 pp239ndash247 1970

[73] K Ito T Onishi H Takeda et al ldquoSimultaneous formation ofNiAl ohmic contacts to both n- and p-type 4H-SiCrdquo Journal ofElectronic Materials vol 37 no 11 pp 1674ndash1680 2008

[74] Electronic Archive New Semiconductor Materials Charac-teristics and Properties httpwwwiofferuSVANSMSemic-ondSiCbandstrhtml

[75] M Y Zaman D Perrone S Ferrero L Scaltrito and MNaretto ldquoEvaluation of correct value of Richardsonrsquos constantby analyzing the electrical behavior of three different diodes atdifferent temperaturesrdquo Materials Science Forum vol 711 pp174ndash178 2012

[76] S A Reshanov K V Emtsev F Speck et al ldquoEffect of anintermediate graphite layer on the electronic properties ofmetalSiC contactsrdquo Physica Status Solidi B Basic Research vol245 no 7 pp 1369ndash1377 2008

[77] W Lu W C Mitchel G R Landis T R Crenshaw and W ECollins ldquoCatalytic graphitization and Ohmic contact formationon 4HndashSiCrdquo Journal of Applied Physics vol 93 no 9 pp 5397ndash5403 2003


[78] A C Ferrari and J Robertson ldquoInterpretation of Raman spectraof disordered and amorphous carbonrdquo Physical Review BmdashCondensed Matter and Materials Physics vol 61 no 20 pp14095ndash14107 2000

[79] A C Ferrari and J Robertson ldquoRaman spectroscopy ofamorphous nanostructured diamond-like carbon and nan-odiamondrdquo Philosophical Transactions of the Royal Society AMathematical Physical and Engineering Sciences vol 362 no1824 pp 2477ndash2512 2004

[80] A C Ferrari J C Meyer V Scardaci et al ldquoRaman spectrumof graphene and graphene layersrdquo Physical Review Letters vol97 no 18 Article ID 187401 2006

[81] C H Lui Z Li Z Chen P V Klimov L E Brus and T F HeinzldquoImaging stacking order in few-layer graphenerdquo Nano Lettersvol 11 no 1 pp 164ndash169 2011

[82] W Norimatsu and M Kusunoki ldquoSelective formation of ABC-stacked graphene layers on SiC(0001)rdquo Physical Review B vol81 no 16 Article ID 161410 2010

[83] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabaticeffectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007

[84] R Li Z Guo J Yang X Zeng and W Yuan ldquoInvestigationof TaNi bilayered ohmic contacts on n-type SiC single-crystalsubstraterdquoMonatshefte fur Chemie vol 143 no 9 pp 1329ndash13342012

[85] A V Kuchuk M Guziewicz R Ratajczak M Wzorek V PKladko and A Piotrowska ldquoLong-term stability of Ni-silicideohmic contact to n-type 4H-SiCrdquo Microelectronic Engineeringvol 85 no 10 pp 2142ndash2145 2008

[86] A V Kuchuk M Guziewicz R Ratajczak M Wzorek V PKladko and A Piotrowska ldquoThermal degradation of AuNi

2Si

n-SiC ohmic contacts under different conditionsrdquo MaterialsScience and Engineering B vol 165 no 1-2 pp 38ndash41 2009

[87] A V Kuchuk M Guziewicz R Ratajczak M Wzorek V PKladko and A Piotrowska ldquoReliability tests of Au-metallizedNi-based ohmic contacts to 4H-n-SiC with and withoutnanocomposite diffusion barriersrdquo Materials Science Forumvol 645ndash648 pp 737ndash740 2010

[88] M A Borysiewicz E Kaminska M Mysliwiec et al ldquoFun-damentals and practice of metal contacts to wide band gapsemiconductor devicesrdquo Crystal Research and Technology vol47 no 3 pp 261ndash272 2012

[89] S Liu Z He L Zheng et al ldquoThe thermal stability study andimprovement of 4H-SiC ohmic contactrdquoApplied Physics Lettersvol 105 no 12 Article ID 122106 2014

[90] B Barda P Machac S Cichon and M Kudrnova ldquoThermaldegradation of Ni-based Schottky contacts on 6HndashSiCrdquoAppliedSurface Science vol 257 no 9 pp 4418ndash4421 2011

[91] C Yue Z Gao-Jie L Yi-Hong S Yu-Jun W Tao and CZhi-Zhan ldquoEffect of the annealing temperature on the long-term thermal stability of PtSiTaTi4HndashSiC contactsrdquo ChinesePhysics B vol 24 no 10 Article ID 107303 2015

[92] D P Hamilton M R Jennings C A Fisher Y K Sharma S JYork and P A Mawby ldquoCharacteristics and aging of SiCMOS-FETs operated at very high temperaturesrdquoMRSProceedings vol1693 2014

[93] A V Kuchuk J Ciosek A Piotrowska et al ldquoBarrier propertiesof Ta-Si-N films in Ag-and Au-containing metallizationrdquo Vac-uum vol 74 no 2 pp 195ndash199 2004

[94] A V Kuchuk E Kaminska A Piotrowska et al ldquoAmorphousTandashSindashN diffusion barriers on GaAsrdquoThin Solid Films vol 459no 1-2 pp 292ndash296 2004

[95] A V Kuchuk V P Kladrsquoko V F Machulin and A PiotrowskaldquoThermal stability of thin amorphous Ta-Si-N films used inAuGaN metallizationrdquo Technical Physics vol 51 no 10 pp1383ndash1385 2006

[96] R A Serway Principles of Physics Saunders College PublishingFort Worth Tex USA 2nd edition 1998

[97] M W Cole P C Joshi C Hubbard J D Demaree andM Ervin ldquoThermal stability and performance reliability ofPtTiWSiNi ohmic contacts to n-SiC for high temperature andpulsed power device applicationsrdquo Journal of Applied Physicsvol 91 no 6 pp 3864ndash3868 2002

[98] A Virshup L M Porter D Lukco K Buchholt L Hultmanand A L Spetz ldquoInvestigation of thermal stability and degrada-tion mechanisms in Ni-based ohmic contacts to n-type SiC forhigh-temperature gas sensorsrdquo Journal of Electronic Materialsvol 38 no 4 pp 569ndash573 2009

[99] J S Park K Landry and JH Perepezko ldquoKinetic control of sili-con carbidemetal reactionsrdquoMaterials Science and EngineeringA vol 259 no 2 pp 279ndash286 1999

[100] L Han H Shen K Liu et al ldquoImproved adhesion and interfaceohmic contact on n-type 4H-SiC substrate by using NiTiNirdquoJournal of Semiconductors vol 35 no 7 Article ID 072003 2014

[101] MXu XHu Y Peng et al ldquoFabrication of ohmic contact on thecarbon-terminated surface of n-type silicon carbiderdquo Journal ofAlloys and Compounds vol 550 pp 46ndash49 2013

[102] D M Fleetwood E X Zhang X Shen C X Zhang R DSchrimpf and S T Pantelides ldquoBias-temperature instabilitiesin silicon carbide MOS devicesrdquo in Bias Temperature Instabilityfor Devices and Circuits pp 661ndash675 Springer New York NYUSA 2014

[103] G Adamo A Tomasino A Parisi et al ldquoElectrooptical charac-terization of new classes of silicon carbide UV photodetectorsrdquoIEEE Photonics Journal vol 6 no 6 Article ID 0600707 2014

[104] D Prasai W John LWeixelbaum et al ldquoHighly reliable siliconcarbide photodiodes for visible-blind ultraviolet detector appli-cationsrdquo Journal of Materials Research vol 28 no 1 pp 33ndash372013

[105] R Chand M Esashi and S Tanaka ldquoP-N junction and metalcontact reliability of SiC diode in high temperature (873 K)environmentrdquo Solid-State Electronics vol 94 pp 82ndash85 2014

[106] S Tanimoto M Miyabe T Shiiyama et al ldquoToward a betterunderstanding of Ni-based ohmic contacts on SiCrdquo MaterialsScience Forum vol 679ndash680 pp 465ndash468 2011

[107] P Borowicz A Kuchuk Z Adamus et al ldquoVisible and deep-ultraviolet Raman spectroscopy as a tool for investigation ofstructural changes and redistribution of carbon in Ni-basedOhmic contacts on silicon carbiderdquo ISRN Nanomaterials vol2012 Article ID 852405 11 pages 2012

[108] A Kuchuk V Kladko Z Adamus et al ldquoInfluence of carbonlayer on the properties of Ni-based ohmic contact to n-type 4H-SiCrdquo ISRNElectronics vol 2013 Article ID 271658 5 pages 2013


[110] S Cichon P Machac B Barda and M Kudrnova ldquoSi ohmiccontacts on N-type SiC studied by XPSrdquo Microelectronic Engi-neering vol 106 pp 132ndash138 2013


[111] F A Mohammad Y Cao and L M Porter ldquoOhmic contacts tosilicon carbide determined by changes in the surfacerdquo AppliedPhysics Letters vol 87 no 16 Article ID 161908 pp 1ndash3 2005

[112] Y M Basin V M Kuznetsov V T Markov and L S GuzeildquoPhase-equlibria in the Ni-Si-C systemrdquo Russian Metallurgyvol 4 pp 197ndash200 1988

[113] M Vivona G Greco F Giannazzo et al ldquoThermal stability ofthe current transport mechanisms in Ni-based Ohmic contactson n- and p-implanted 4H-SiCrdquo Semiconductor Science andTechnology vol 29 no 7 Article ID 075018 2014

Submit your manuscripts athttpwwwhindawicom

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ohmic contacts to n-type 4H-SiC with an emphasis on high-temperature handling capability

There exist several review articles on contacts to SiC [4ndash6] however in the last few years many new peer-reviewedpapers on metalSiC contacts were published often contain-ing contradicting results and conclusions but no consensushas been reachedTherefore the aim of this work is to presentbriefly the last key results on the matter and to post openquestions concerning the unclear issues of ohmic contacts ton-type SiC

2 Ohmic Contacts to 4H-n-SiCState of the Art

For metal contacts to n-type 4H-SiC the electron affinity(119883119904) and work function of the metal (119882

119898) are the relevant

quantities determining the Schottky barrier height120593119861= 119882119898minus

119883119904 due to a sufficiently lowdensity of surface states in 4H-SiC

(sim1012 cmminus2 eVminus1) Thus according to the Schottky theorythe barrier height 120593

119861of a metal4H-n-SiC strongly depends

on the electron work function 119882119898of the metals Indeed as

is shown in Figure 1 the experimental results of metal4H-n-SiC contacts confirm this model [7ndash23]

As is well known a rectifying (Schottky) metal contactto n-type semiconductor is formed when the electron workfunction of the metal exceeds the electron affinity of thesemiconductor (119882

119898gt 119883119904) and the ohmic contact is formed

if119882119898le 119883119904 Since119882

119898for most metals exceeds the electron

affinity 119883119904of 4H-SiC (see Figure 1) the formation of ohmic

contacts to 4H-n-SiC is typically done by the deposition ofthe same metals as for the Schottky barriers however withsubsequent high-temperature annealing Such rapid thermalannealing (RTA) causes (i) the creation of a tunnel contactwhich consists of a thin barrier obtained by heavy doping ofthe semiconductor throughwhich carriers can readily tunneland (ii) the formation of new compounds which reduces thebarrier height and the width of the depletion region at themetal-semiconductor interface It should be noted that thispaper is focusedmainly on Si-face 4H-SiCmaterial Howeverthe SiC surface polarity (Si-face or C-face) and polytypes(3C 2H 6H etc) are important considerations for ohmiccontact formationThe polarity and polytypes can lead to thedifference in barrier height and interaction at the metalSiCinterface for the same metallization scheme [24] Thus bothof them strongly influence the electrical quality of the contact

On the basis of previous works [26ndash45] the commonprocesses in the reaction of metals with SiC can be identifiedas follows (i) SiC + refractory metals (Ti Ta W etc) rarrRTArarr carbides (TiC TaCWC etc) + silicides (TiSix TaSixWSix etc) + ternary phases (TiCSix TaCSixWCSix etc) (ii)SiC + othermetals (Ni Pd Pt etc)rarrRTArarr silicides (NiSixPdSix PtSix etc) + C

The fabrication of ohmic contacts to SiCmay be achievedusing various metallization schemes and for the n-typeSiC Ni and Ni-based contacts are most commonly usedThese contacts are formed by high-temperature annealingat temperatures in the range 900ndash1100∘C and their specificcontact resistance lies typically in the range 10minus4ndash10minus6Ωcm2

Electron work function Wm (eV)

Cu

CrW Ni

Ti

Al

Mo

Au

Pd Pt

Ir

20

18

16

14

12

10

08

06

04

02

0040 45 50 55

ExperimentalTheoretical (X4H-SiC

s = 36 eV)

Barr

ier h

eigh

t120593B

(eV

)

Figure 1 Experimental dependence of the barrier height 120593119861of

metal4H-n-SiC on the electron work function 119882119898of the metals

[7ndash23] Red curve-theoretical dependence according to the Schottkytheory (the electron affinity of 4H-SiC119883

119904= 36 eV [25])

[26ndash38] The physical properties of Ni and the main NixSi1minusxphases used in metallization scheme for SiC are listed inTable 1 [46ndash48]

Many experimental studies have been performed in orderto understand the mechanism of ohmic contact formationand different models were proposed to explain the Schottkyto ohmic transition however the final picture is still farfrom being complete Indeed in spite of a large numberof publications and progress in the study of Ni and SiCinteraction there are still many open questions connectedto the mechanism of contact formation and their reliabilityThere are different explanations in the literature concerningthe mechanisms of ohmic contact formation namely (i) theformation of silicides [35 39] or carbon precipitates [28 40](ii) inhomogeneity of the metalSiC Schottky barrier [41](iii) creation of carbon vacancies [42 43] or defect states[44] near the interface region and (iv) snowplow effect ofdopants in the SiC substrate [45] On the other hand ithas been commonly observed that the formation of ohmiccontacts is accompanied by the interfacial reaction andor SiCdecomposition

There is no doubt that Ni can very easily react withSiC forming a whole spectrum of nickel silicides dependingon the details of the ohmic contact fabrication process Onthe other hand there is strong evidence that the fabricationof silicides via a contact reaction of Ni with SiC or via adeposition of the specific silicide is not enough to produce anohmic contact with low specific resistance This is especiallytrue for Ni

2Si which was firstly proposed to be responsible for

the ohmic behavior but later shown to form Schottky barrierswith height of 162ndash175 eV [41] Also a question arises aboutthe fate of the remaining carbon which may segregate in thecontact region





119898(eV)













3 Experimental


4OH H

2O2 H2O = 1 1 5 at







2plasma





35Si15N50










4 Results



2








2





2Sin-







119888sim 55 times





I(A

)

U (V)




03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2


(a) FL-Ni

I(A

)

U (V)


02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2





(b) FL-Si

I(A

)


003

002

001

000

minus001

minus002




(c) FL-Ni

I(A

)


003

002

001

000

minus001

minus002

minus003




(d) FL-Si

I(A

)


0004

0003

0002

0001

0000

minus0001

minus0002

minus0003




(e) FL-Ni

I(A

)


0015

0010

0005

0000

minus0005

minus0010




(f) FL-Si



SiSiC SiNi2Si

NiRB

S yi

eld

(au

)


400 500 600 700

18

16

14

12

10

8

6

4

2

0



(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)


2Si with

FL-Ni [26]













2SiSiC











2Si to NiSi

2contacts








2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics







119898(eV)













3 Experimental


4OH H

2O2 H2O = 1 1 5 at







2plasma





35Si15N50










4 Results



2








2





2Sin-







119888sim 55 times





I(A

)

U (V)




03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2


(a) FL-Ni

I(A

)

U (V)


02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2





(b) FL-Si

I(A

)


003

002

001

000

minus001

minus002




(c) FL-Ni

I(A

)


003

002

001

000

minus001

minus002

minus003




(d) FL-Si

I(A

)


0004

0003

0002

0001

0000

minus0001

minus0002

minus0003




(e) FL-Ni

I(A

)


0015

0010

0005

0000

minus0005

minus0010




(f) FL-Si



SiSiC SiNi2Si

NiRB

S yi

eld

(au

)


400 500 600 700

18

16

14

12

10

8

6

4

2

0



(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)


2Si with

FL-Ni [26]













2SiSiC











2Si to NiSi

2contacts








2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





35Si15N50










4 Results



2








2





2Sin-







119888sim 55 times





I(A

)

U (V)




03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2


(a) FL-Ni

I(A

)

U (V)


02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2





(b) FL-Si

I(A

)


003

002

001

000

minus001

minus002




(c) FL-Ni

I(A

)


003

002

001

000

minus001

minus002

minus003




(d) FL-Si

I(A

)


0004

0003

0002

0001

0000

minus0001

minus0002

minus0003




(e) FL-Ni

I(A

)


0015

0010

0005

0000

minus0005

minus0010




(f) FL-Si



SiSiC SiNi2Si

NiRB

S yi

eld

(au

)


400 500 600 700

18

16

14

12

10

8

6

4

2

0



(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)


2Si with

FL-Ni [26]













2SiSiC











2Si to NiSi

2contacts








2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




I(A

)

U (V)




03

02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2


(a) FL-Ni

I(A

)

U (V)


02

01

00

minus01

minus02

minus03

minus2 minus1 0 1 2





(b) FL-Si

I(A

)


003

002

001

000

minus001

minus002




(c) FL-Ni

I(A

)


003

002

001

000

minus001

minus002

minus003




(d) FL-Si

I(A

)


0004

0003

0002

0001

0000

minus0001

minus0002

minus0003




(e) FL-Ni

I(A

)


0015

0010

0005

0000

minus0005

minus0010




(f) FL-Si



SiSiC SiNi2Si

NiRB

S yi

eld

(au

)


400 500 600 700

18

16

14

12

10

8

6

4

2

0



(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)


2Si with

FL-Ni [26]













2SiSiC











2Si to NiSi

2contacts








2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




SiSiC SiNi2Si

NiRB

S yi

eld

(au

)


400 500 600 700

18

16

14

12

10

8

6

4

2

0



(a)

SiSiC SiNi2Si

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi2Si (FL-Ni)

400 500 600 700

18

16

14

12

10

8

6

4

2

0



(b)


2Si with

FL-Ni [26]













2SiSiC











2Si to NiSi

2contacts








2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





2bulk materials




















2Sin-





2Si orthorhombic



















2Sin-SiC












n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics










n-SiCNi

XRD

inte

nsity

(au

)

2120579 (deg)

SiC (0004)

(111) (200)(013) (020)

Ni

120575-Ni2Si

35 40 45 50 55

104

103

102


(a)

SiSiC

Ni

RBS

yiel

d (a

u)

Channel number

n-SiCNi

400 500 600 700

18

16

14

12

10

8

6

4

2

0

1050∘C



(b)







2Si






013119868020




013119868020












XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




XRD

inte

nsity

(au

)

2120579 (deg)

104

103

102


42 44 46 48 50 52 54

(111)(013)

(220)(300)

(020)

1100∘C

1050∘C

950∘C

600∘C

As-deposited

(a)

120575-Ni2Si

10

1

I 013I

020(N

i 2Si)


055

050

045

040

035600 850 900 950 1000 1050 1100

FWH

M(013)N

i 2Si(∘)

(b)


2Si texture (119868

013119868020

) andFWHMof (013)Ni


013119868020


50nm

50nm

03120583m

15 120583m

Hsim 65nm

Hsim 8nm

(a)

50nm

50nm

03120583m

15 120583m

Hsim 13nm

Hsim 70nm

(b)

50nm

03120583m

15 120583m

02120583m

Hsim 44nm

Hsim 60nm

(c)

03120583m

15120583m

05120583m

75 120583m

Hsim 150

nm

Hsim 200nm

(d)








c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




c

TEM

200nm

(a)

XEDS NiSi

c

(b)

2 (1nm)

0001

0000

SAED1120

[1100]

Ni31Si12

(c)

5 (1nm)

000

[011]NBD

Ni2Si

011

111

(d)




31Si12


2Si phase TEM







1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




1100nm

(a)

2

11120583m

(b)

1100nm

(c)

1

21120583m

(d)







2Si




2Si






2Si









2 15min) and






119888for Ni

2Sin-SiC ohmic




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Amorphous

[0001]

2nm[1120]

[1100]4H SiC

(a)

[0001]

2nm 4H SiC

199Aring

[1010][1210]

(b)



10minus3

10minus4

10minus5

r c(Ω

cm2 )


6min12min


2Si ohmic





minus5Ωcm2 of




2Si ohmic



120575-Ni2Si

I 013I

020(N

i 2Si)

r c(Ω

cm2 )

10

1

20

15

10

05

times10minus4


2Si4H-n-SiC ohmic


013119868020






00given by

[72]

11986400=119902ℎ

4120587radic119873119889

119898lowast120576 (1)



11986400


00119896119879 ≫ 1) thermionic



r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




r c(Ω

cm2 )

100

101

10minus1

10minus2

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8

1015 1016 1017 1018 1019 1020


Nd (cmminus3)

120593B = 05 eV

120593B = 045 eV

120593B = 04 eV120593B = 035 eV

120593B = 03 eV

Our results

(a)



6min12min

120593 B(e

V)

055

050

045

040

035

030

(b)





2Si ohmic contacts




and 120576 = 9661205760 11986400








119903119888=119896119879


120593119861

119896119879) (2)



calculated by [73]

119903119888=

1198962

119902119860lowastradic120587 (120593119861+ 119906119865) 11986400

cosh (11986400

119896119879)radiccoth(

11986400

119896119879)

sdot exp(120593119861+ 119906119865

1198640

minus119906119865

119896119879)

(3)

where 1198640= 11986400coth(119864

00119896119879) and 120583 = 119896119879 ln(119873

119888119873119889) where






119861)


119888for Ni and








2Si










Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Inte

nsity

(au

)



1191

1587

1707

750

600

450

300

150

01200 1300 1400 1500 1600 1700 1800


(a)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

150

100

50

0

1361

1476

1597

1714


(b)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

450

300

150

0

1194

1366

1522

1584

1703


(c)

Inte

nsity

(au

)



1200 1300 1400 1500 1600 1700 1800

800

600

400

200

0

1170

1360

1469

1586

1666


(d)


600∘C15min (c) 950∘C3min (d) 1050∘C3min






tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




tens

ity (a

u)



1100 1200 1300 1400 1500 1600 1700

800

1000

600

400

200

0

1349

1362 1569

1582

1613
























2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics













2Sin-SiC


2Sin-SiC









2Sin-SiC contact









2Sin-SiC contact


2Sin-






2Sin-














119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





119886





119886










2Sin-





2Sin-SiC On the






2Sin-SiC










35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics







35Si15N50Ni2Sin-SiC









2Si and Au layers




35Si15N50




2Sin-SiC contacts


2Sin-






2Sin-





2Si







2Sin-SiC


2Sin-SiC





119909(NiSi)






2Si and





2Sin-





2Sin-SiC stacks



Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(a)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuNi2Sin-SiC


(b)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2

AuTaSiNNi2Sin-SiC


(c)

Curr

ent (

A)

Voltage (V)

04

02

00

minus02

minus04

minus2 minus1 0 1 2


AuTaSiNNi2Sin-SiC

400∘Cair150h

(d)



treatments














XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




XRD

inte

nsity

(au

)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si

Ni31Si12


Au

Ni(111)

(111) (200)

(013) (020)

(300)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

(a)XR

D in

tens

ity (a

u)

2120579 (deg)

106

105

104

103

102

101

120575-Ni2Si


Au (111) (200)

(013) (020)

36 38 40 42 44 46 48 50

SiC

(000

4)

Au

AuTaSiNNi2Sin-SiC

(b)




RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

x5

(a)


RBS

yiel

d (a

u)

Energy (keV)400 800 1200 1600 2000

100

75

50

25

0

Oo

Nio

Sio

Auo

Tao

AuTaSiNNi2Sin-SiC

x5

(b)











As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




As-deposited

10120583m

(a) 800∘CAr3min

10120583m

(b) 400∘Cair150 h

As-deposited

10120583m

(c) 800∘CAr3min

10120583m

(d) 400∘Cair150 h




























2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics










2Si phase on n-




2Si grains




2Si









Competing Interests


Acknowledgments


References















4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





4H-SiC



















































































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



















































2Si



































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics












FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



research article ni-based ohmic contacts to n -type 4h-sic ...research article ni-based ohmic...

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