review article physics of internal photoemission … of internal...review article physics of...

Review ArticlePhysics of Internal Photoemission and Its Infrared Applicationsin the Low-Energy Limit

Y F Lao1 and A G U Perera12

1Department of Physics and Astronomy Georgia State University Atlanta GA 30303 USA2Center for Nano-Optics (CeNO) Georgia State University Atlanta GA 30303 USA

Correspondence should be addressed to A G U Perera upereragsuedu

Received 13 September 2015 Accepted 29 December 2015

Academic Editor Jung Y Huang

Copyright copy 2016 Y F Lao and A G U PereraThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Internal photoemission (IP) correlates with processes in which carriers are photoexcited and transferred from one material toanother This characteristic allows characterizing the properties of the heterostructure for example the band parameters of amaterial and the interface between two materials IP also involves the generation and collection of photocarriers which leads toapplications in the photodetectorsThis review discusses the generic IP processes based on heterojunction structures characterizing119901-type band structure and the band offset at the heterointerface and infrared photodetection including a novel concept ofphotoresponse extension based on an energy transfer mechanism between hot and cold carriers

1 Introduction

Internal photoemission (IP) spectroscopy is an attractivemethod [1ndash4] for studying the properties of materials andoptical processes that take place at the interface of two mate-rials IP refers to such a case where carriers are photoexcitedand transferred from one material to another by passingthrough an interface Photoexcitation occurs in the absorber(referred to as IP emitter) before photoemission The pho-toexcited holes with high energies originate from those at thestates around the Fermi level By having higher energy thanthe photoemission threshold these carriers can come acrossthe penitential barrier in other words photocarriers mustbe transferred from the energy band of the emitter to thatof the barrier material This process typically involves scat-terings through which the excited holes are directed to passover the emitter-barrier interface Optical excitation includesdirect and indirect transitions The type of transitions thatcontributes to quantum yield (defined as number of carriersbeing collected per incident photon) relies on the energy ofthe incident photon In the vicinity of the photoemissionthreshold carriers must stay at states with energies nearly atthe same level of the potential barrier before emission Thisresults in a higher probability of the occurrence of indirect

transitions However under the excitation of photons withenergies much greater than the threshold energy direct tran-sitions dominate over the indirect transitions in contributingthe quantum yield significantly Although many of IP studieswere reported before [1] IP is still attractive in particularwith recent demonstration of its advantages in characterizingnew material systems [3 4] Based on the above-mentionedprinciple the use of the IP effect lies in at least the followingareas (1) studying the band parameters of materials suchas the band structure (2) studying the band offset at theinterface of a heterostructure (3) development of IP-basedphotodetectors

The internal photoemission is characterized by the quan-tum yield [2] which can be obtained as being the multi-plication of 119877 and ℎ] where 119877 and ℎ] are the responsivityand the energy of the photon respectively Photoresponsein the energy regime near the IP threshold comes withtwo features determined by the optical transitions in theactive region which create photocarriers and the escapeof photocarriers which leads to photocurrents The escapecapability can be mitigated by the loss in the energy orredirection of the carrier as a result of scatteringwith phononThe onset of the carrier-phonon scattering depends on theexcess kinetic energy of photocarriers [1] It is expected

Hindawi Publishing CorporationAdvances in OptoElectronicsVolume 2016 Article ID 1832097 18 pageshttpdxdoiorg10115520161832097

2 Advances in OptoElectronics

(1) (2)

Emitter

hh

hh

lh

lhBarrier

(ii) (i)

(1)(2)VB

Ef

Ef

p-emitter i-barrier

120588(120598 minusEf) middot f(120598)

(a)

PBAwithout tail

PBA with aGaussian tail

DOS DOS

Ener

gy

EfEf

(b)

Figure 1 (a) Schematic band diagram of a 119901-emitter119894-barrier structure 120588(120598 minus119864119891)119891(120598) is the multiplication of the energy distribution (120588)and the FD function (119891) (i) and (ii) correspond to the nondegenerate and degenerate doping respectively IP processes labeled as (1) and(2) consist of optical transitions in the emitter and the escaping of holes from the emitter to the barrier (b) DOS with and without the bandtailing effect

that this occurs at the above-threshold regime and afterexcitation the excess kinetic energy of carriers should begreater than the phonon energy Upon scatterings a portionof photocarriers could remain in the absorber unable toescape which leads to degradation in the photoresponse Adetailed study on this should benefit future improvementof the device performance The IP approach studying thescattering effects has been recently demonstrated [8] throughfitting of the near-threshold quantum yield spectra

In an IP experiment photoemitted carriers are col-lected and detected as a photocurrent varying with thephoton energy The IP effect for photodetection requiresthe use of a heterostructure An important concept recentlydemonstrated [9] is the photoresponse extension triggeredby introducing a hot-cold carrier energy mechanism Thephotoresponse is substantially extended without the need ofreducing the IP threshold energy

In this review we discuss the IP spectroscopy as amethodto characterize semiconductors and heterostructures and usethe IP effect to develop photodetectors

2 IP Characterization of Band Parameters

21 TheTheory of the IP Spectroscopy The theoretical basis ofIP was initially reported in Fowlerrsquos works [13] on externalphotoemission of electrons (from metal to vacuum) Theoriginal form of the quantum yield 119884 can be expressed as

119884 sim 119891 (120583) sdot (119896119879)2 (1)

which contains a 119879-dependent term 119891(120583) has the followingexpression [13]119891 (120583)

=

119890120583minus1198902120583

4+1198903120583

9minus sdot sdot sdot (120583 ⩽ 0)

1205872

6+1205832

2minus (119890minus120583minus119890minus2120583

4+119890minus3120583

9minus sdot sdot sdot ) (120583 ⩾ 0)

(2)

where 120583 equiv (ℎ] minus Δ)119896119879 and ℎ] is the photon energy Fowlerrsquosyield function can be actually reduced [14] to be independentof 119879 when ℎ] gt Δ + 3119896119879 that is

119884 (ℎ]) sim (ℎ] minus Δ)2 (3)

Fowlerrsquos yield function is mainly used to fit the IP thresholdsDespite the fact that Fowlerrsquos yield function was originallyderived for external photoemission it has been applied [15]to many IP cases By taking into account the fact thatsemiconductors have a different band structure compared tometal exponent ldquo2rdquo in (3) is replaced with a parameter 119901 [16ndash19]The value of 119901was reported varying between 1 and 3 [19]By taking 119901 as a fitting parameter the physical meaning ofthe yield function becomes unclear Furthermore the effectof the temperature on the IP process is ignored which couldcause underestimate of Δ This result is significant when theyield function applied to the low-energy limit for example inthe energy range of lt1 eV

To obtain accurate IP thresholds temperature-dependentIP spectroscopy (TDIPS) has been developed Figure 1(a)shows the TDIPS principle for a 119901-type structure whichincludes two doping concentrations under which 119864119891 can befound to be (i) above and (ii) below the top of the valenceband (VB) By absorbing photons photoexcited holes withhigh energies from the emitter escape over the potentialbarrier The photoemission process of carrier transport fromthe emitter to the barrier is shown in the inset of Figure 1(a)During this process there exist photon absorption and scat-terings The scattering is crucial for the photoexcited holesto be transferred across the emitter-barrier interface Bothdirect and indirect transitions can lead to photoexcitation andhave the primary contributions to the IP yield in the energyregime near and greater than the IP threshold respectively

To obtain the band offsets the line shape of the spectralquantum yield should be considered It should be noted thatthe IP yield concerns with the primary processes includingthe carriersrsquo energies and the escape probabilities of thesecarriers which can be evaluated by considering the photoex-citation of holes via intervalence band (IVB) transitions [12](120588(120598 ℎ]minus119864119891)) and the escape of the holes (119875(120598 Δ)) [20]Theseconsiderations lead to the following expression119884 (ℎ]) = 1198840 (119896119879)

+ 1198620 int

infin

Δ119891 (120598 ℎ]) 120588 (120598 ℎ] minus 119864119891) 119875 (120598 Δ) 119889120598

(4)

where 120588(120598 ℎ] minus 119864119891) is an energy distribution function and119875(120598 Δ) a probability function1198620 is a constant 120598 is the energy

Advances in OptoElectronics 3

of the holeΔ is the barrier height corresponding to an energydifference between the Fermi level and the barrier Equation(4) is deduced in terms of the degenerate (highly) dopedemitters by changing the sign of 119864119891 it can be used fornondegenerate doping The Fermi-Dirac (FD) statistics tellthat carriers are at the energy states above the Fermi level atfinite temperatures To this end119891(120598 ℎ]) = [1+119890(120598minusℎ])119896119879]minus1 isused to describe the the distribution of carriers provided thatthe energy states of photoexcited holes are the same as thosebefore photoexcitation

Equation (4) contains a term 1198840 which is the backgroundsignal for example the thermionic background It can bedetermined by giving 1198840 the value of the experimental yieldin the energy range less than the value of Δ

The function 119875(120598 Δ) is calculated by an escape-conemodel [20 21] For a successful escaping over a barrierthe normal (to the interface) momentum of carriers mustbe greater than the potential barrier Correspondingly theenergy states on a spherical Fermi cap in the k space areaccounted to calculate 119875(120598 Δ) which gives a value propor-tional to (120598 minus Δ) for 120598 ge Δ and 0 for 120598 lt Δ

The energy distribution [120588(120598 1205980)] of photocarriers hasa primary influence on the quantum yield By consideringthe fact that the direct transitions are associated with thejoint density of states (JDOS) and indirect transitions aremainly determined by the occupation of initial states [22]the density of states (DOS) of the VB can be used for 120588(120598 1205980)For the transitions taking place near the Γ point the use ofthe parabolic-band approximation (PBA) leads to 120588(120598 1205980) sim(120598 minus 1205980)

12As the emitters are doped the IP model should also take

into account the doping-inducted effects for example theband tailing states Potential fluctuations can be induced bydopants leading to band tailing states at the top of the VB Asshown in Figure 1(b) the Kane model [23] is used to modifythe PBA DOS Dopants-induced changes in DOS have aprimary influence on the quantum yield near the energy ofthe IP threshold the quantum yield is increased for ℎ] gt

119864119891 + Δ as a consequence of contribution from the states inthe forbidden gap and is slightly reduced for ℎ] lt 119864119891+ΔTheconsequence of this is the smaller Δ determined by fitting tothe yield spectra

The process to determine the IP threshold is primarilyinfluenced by the IP probability119875(120598 Δ) In addition120588(120598 1205980) isassociated with the optical transitions By taking into accountthe slowly varying nature of 119891 and 119875 and thus the primaryeffect of 120588 on the yield the derivative can be obtained as119889119884119889(ℎ]) sim 120588(Δ minus ℎ] 119864119891) Therefore the second derivative

1198892119884

119889 (ℎ])2sim119889 (JDOS)119889 (ℎ])

(5)

where 120588 can be obtained using JDOS when direct IVB tran-sitions are considered This indicates a relationship betweenthe band structure and the IP yield

22 IP Determination of the Spin-Orbit Splitting and theParticipation of Phonons in Indirect Intervalence Band Transi-tions As shown in Figure 2(a) indirect transitions take place

via an intermediate state which can be in the same VB orin a nearby band The phonon-assisted indirect interbandabsorption can be easilymeasured [24 25] However phononparticipating in indirect IVB transitions is difficult to bemeasured because it is usually featureless [26 27] (egFigure 2(b)) IP takes place when the photoexcited carriers(in the photon absorber (emitter)) have the kinetic energiesgreater than the barrier [2] To escape these photoexcitedcarriers must transmit from the absorber to the barrierBecause of this indirect transitions can lead to remarkablefeatures due to their higher probabilities of occurrence thanthe direct transitions [22]

The quantum yield spectra of different 119901-type GaAsAlGaAs samples with different Al fractions are shown inFigure 2(c) which shows the quantum yield spectra It canbe seen that these samples have similar spectral profilesbetween 03 and 045 eV The fluctuations at energies greaterthan 045 eV are due to optical interference It is noted thatthe features between 03 and 045 eV are independent of thebiases the height and the shape of the potential barrierThesefeatures can be considered to be related to the SO-HH holetransitions

The differentiated quantum yield spectra are shown inFigures 3(a)ndash3(c) Different features observed have the onsetin consistence with the double-differential peaksThe peak atsim034 eV on the second derivative spectra has the correlationwith the SO-HH singularity The verification of this canbe done by calculating 1nabla119896sum119894119895[119864119894(k) minus 119864119895(k)] as shownin Figure 3(d) The weak feature of the SO-HH singularityagrees with the experimental data

The value of Δ 0 can be determined [28 29] by resolvingthe critical points (interband transitions) 1198640 and 1198640 + Δ 0which correspond to the HH to CB transition and the SOto CB transition respectively In contrast to this a directdetermination of Δ 0 is advantageous to the studies of itsvariation with the doping concentration (Figure 3) andtemperature (Figure 4(a)) Figure 4(b) shows the determinedvalues that nearly remain the same with an average of03392 plusmn 00003 eV The result agrees with reported valuesin the past that is 0390ndash0341 eV [30ndash32] It is difficult todetermine the doping dependency of the Δ 0 by using theinterband transitions [27] because DOS at the Γ point canbe significantly modified by the band tailing states Howeverthe value of Δ 0 can be obtained by the two-thirds rule [ieΔ 1 = (23)Δ 0] [33] by which a constant Δ 0 can be foundfrom the synchronous variation of the interband criticalpoints 1198641 (HH to CB) and 1198641 + Δ 1 (LH to CB) (at larger k)with doping concentrations [34]

The energies of various phonons can be determined by theinternal photoemission spectroscopy Figure 3(a) shows thetwo strong features at sim037 eV and 044 eV By consideringthat the features correspond to the energies of Δ 0 + 119864ph(where119864ph is the phonon energy) these two features correlatewith LO(Γ) and 3 times TO(Γ) Following a similar procedure avariety of phonons can be determined as shown in Table 1 Itshould be noted that themost important phonons LO(Γ) and3 times TO(Γ) have the significant contributions to the quantumyield The result was also observed in previous studies on thehole-optical phonon interactions [35ndash37]


PhononEn

ergy

Band edge

HH

LH

SO

(1)

(2)

(3) (4)

(5)

Ef

EfEB

EB

B

BE

ℏ1205962

ℏ1205961

ℏ1205963

ℏ1205964

111⟩⟩k 100⟩⟩k

(a)

12 9

0

5 6 3

p-type GaAs

Wavelength (120583m)

1 times3 times

120572(103

cmminus1

)1019 cmminus3

1018 cmminus3

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)01 02 03 04 05 06 07

D

A

B

C

D

80KA (6V)

B (6V)

C (6V)

(minus05V)

188nm

188nm

188nm

80nm

015 eV

022 eV

032 eV

032 eV025

eV042

eV

HH rarr LH

HH rarr SO

(c)

Figure 2 (a) Schematic of different intervalence band optical transitions (1)ndash(5) correspond to (1) direct transition (2) direct transition +phonon emission (ℏ1205961) (3) phonon absorption (ℏ1205962) + direct transition (4) direct transition + phonon emission (ℏ1205963) (interband scattering)and (5) phonon absorption (ℏ1205964) + intraband photon absorption Inset plots the optical processes taking place in an emitter(E)barrier(B)heterojunction (b) Optical absorption of 119901-type GaAs (c) Quantum yield spectra of different 119901-type GaAsAl119909Ga1minus119909As heterojunctionsInset shows the flat-band (VB) diagrams [5] at zero bias The doping concentrations are 3 times 1018 cmminus3 (A B and C) and 1 times 1019 cmminus3 (D)The vertical arrows indicate the features that remain the same in different samples

23 IP Studies of the Band Offsets of Type-II InAsGaSbSuperlattice Structure As shown in the 119901B119901 T2SL detector(Figure 5(a)) where two 119901-type InAsGaSb T2SL absorbersresponsible for midlong-wave infrared (MWIRLWIR)absorption are separated by a B-region consisting of anInAsAlSb T2SL different optical transitions can be resolvedby switching the bias polarity as shown in Figure 5(b)Possible transitions include those occurring across theforbidden gaps of the superlattice absorbers (I) the B-region

(II) and the VB offset between the VB of the absorber andthe B-region interface (III) the latter two of which can beobserved in the higher photon energy regime This is shownin the quantum yield (119884) spectra plotted in Figure 5(c)

Fittings to quantum yield spectra in different near-threshold energy regimes were carried out as shown inFigure 5(c) A threshold energy corresponding to one specifictransition is determined by the fact that the band offset hasthe value between the band gaps of absorbers and B-region


Photon energy (eV)03 033 036 039 042 045

Photon energy (eV)

Photon energy (eV)

03 033 036 039 042 045

(a)

(b)

(d)

0008

001

0012

03 033 036 039 042 045

(c)

Sample ABolometer

Sample A (p = 3 times 1018 cmminus3)Sample D (p = 1 times 1019 cmminus3)Sample E (p = 6 times 1019 cmminus3)

AD

E

ADE

dYd

(h)

(au

)d2Y

d(h)

2(a

u)

d2Id(h)2

TA(X

)

TA(L

)

TA(L

)

2times

TA(L

)

LO(X

)

LO(Γ

)

3times

TO(Γ

)

Δ0

Δ0

d(JDOS)d(h)

JDO

S (e

Vminus1Aringminus3 )

log(Y

) (au

)

HH rarr SO VHS

LH rarr SO VHS

inej

]

]Ei(k

)minusEj(k)

1nablaksum

[

Figure 3 (a) Quantum yield (119884) (b) first and (c) second derivatives of quantum yield spectra for samples A (6V 80K) D (minus05V 80K)and E (005V 50) The structure of sample E is the same as A except for its emitter doping concentration (6 times 1019 cmminus3) The verticallines correspond to features listed in Table 1 Also shown in (c) (at the bottom) is bolometer (background) spectra (d) Calculated value of1nabla119896sum119894 =119895[119864119894(k) minus 119864119895(k)] based on a k sdot pmodel [6] The Van Hove singularities (VHS) of intervalence band transitions are indicated

This determines the band gaps (average) of the LWIR andMWIR absorbers to be 0117plusmn 0002 eV and 0157plusmn 0001 eVrespectively agreeing with the nominal values of 0103 eV and0159 eV respectively [41] Based on the obtained VB offset

[0661(plusmn0002) eV] the CB offset between the LWIR absorberand the B-region is determined to be 0004plusmn0004 eV close tothe designed value (0009 eV) [41] Such a small value shouldbarely affect the transport of minority electrons


Photon energy (eV)03 035 04 045

50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300

Reference [30 31 Table III]p = 3 times 1018 cmminus3

p = 1 times 1019 cmminus3p = 6 times 1019 cmminus3

Δ0

(eV

)

(b)

Figure 4 (a) Second yield derivative of the quantum yield spectra at different temperatures (b) Temperature and doping dependence of Δ 0for GaAs Data of Δ 0 adopted from Table 3 of [7] are shown for comparison

Table 1 Phonons of GaAs (80K) determined by internal photoemission spectroscopy Δ 0 is 3392 plusmn 03meVThe numbers in parenthesis areuncertainties

Features (meV) Δ 0 minus 130 Δ 0 minus 74 Δ 0 Δ 0 + 87 Δ 0 + 163

Phonons TA(119883) TA(119871) mdash TA(119871) 2 times TA(119871)Features (meV) Δ 0 + 289 Δ 0 + 354 Δ 0 + 994

Phonons LO(119883) LO(Γ) 3 times TO(Γ)TO(Γ) LO(Γ) LO(119883) TA(119883) TA(119871)

This work (meV) 331 (02) 354 (02) 289 (02) 122 (08) 81 (05)Waugh and Dollinga 332 (03) 354 (08) 299 (06) 975 (006) 770 (006)Blakemoreb 33 355 30 8 mdashGiannozzi et alc 336 361 298 102 78

Steiger et ald 332 361 289 89 88

a[38]bExtracted from multiple phonon features see Table XI of [32]c[39]d[40]

It should be noted that photoemission probabilitiesshould vary in order to fit the band gap or band offset(see Figure 5(c)) With respect to IP at an interface at whichphotocarriers need to overcome a potential barrier 119875(120598 Δ)equals (120598 minus Δ) for 120598 ge Δ and 0 for 120598 lt Δ [2] accordingto an escape-cone model [20] It is apparent however thatphotocarriers excited in the MWIRLWIR T2SL absorbercan freely move towards the direction of photocurrents untilbeing collected This means 100 transmission probabilityThe IP fittings using different 119875(120598 Δ) plotted in Figure 5(c)agree with the above operating mechanism The inset ofFigure 5(c) shows the fitting based on 119875(120598 Δ) = (120598 minus Δ) thatleads to an incorrect spectral profile compared to 119875(120598 Δ) = 1thus not being able to explain the experimental data Theuse of varied 119875(120598 Δ) in consistence with optical processesunder operation is a justification of the applicability of IPspectroscopy to T2SL structures

24 Study of HgCdTe Infrared Photodetectors A schematicof the Hg1minus119909Cd119909TeHg1minus119910Cd119910Te sample is shown inFigure 6(a) consisting of a thin (032 120583m) top Hg068Cd032Telayer and a thick (733 120583m) Hg078Cd022Te absorber grownon the Si substrate Two ohmic contacts are made to theindividual HgCdTe layers Backside illumination was usedfor all of the measurements Figure 6(b) shows the typicalquantum yield spectra at 53 and 78K The undulation isrelated to the optical interference inside the substrate Thelow-energy cut-off is due to the escape of photocarriersfrom the absorber (originating from the optical transitionschematically shown in the inset) Features associated withthe band gap of the Hg068Cd032Te layer which should bearound 028 and 029 eV for 53 and 78K [42] respectivelyare not observed Notice that unlike most semiconductorsthe optical absorption edge of HgCdTe shifts to high energiesat elevated temperatures [42]


GaSb Te substrate

02 120583m T2SL LWIRp-type (4 times 1018cmminus3) contact

21 120583m T2SL LWIRp-type (1 times 1016cmminus3) absorber

100nm T2SL p-type(1 times 1016cmminus3) barrier

20 120583m T2SL MWIRp-type (1 times 1016cmminus3) absorber

05 120583m T2SL MWIRp-type (4 times 1018cmminus3) contact

(a)

I

I

II

II

III

III

Forwardbias

bias

LWIRabsorber absorberB-region

MWIR

Reverse

(b)

02 04 06 08

(I band gap of absorber)

(II band gap of B-region)

(III band offset of LWIR absorberB-region)

01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Exp (minus08V)Exp (08V)Fit

P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 120598 minus ΔP(120598 Δ) = 120598 minus Δ

0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)

Figure 5 (a) Schematic of a pBp type-II InAsGaSb superlattice photodetector (b) Band alignment under forward and reverse biases andthe effective optical transitions that contribute to photocurrents (c) The experimental quantum yield spectra and IP fittings The thresholdsof optical transitions IndashIII can be obtained by fitting different energy regimes Inset comparison of fittings using different transmissionprobabilities

Previous studies have shown that the assumption ofthe parabolic-band approximation (PBA) that is JDOS sim

(120598 minus ℎ])12 is valid for GaAsAlGaAs heterojunctions [2]and type-II InAsGaSb superlattice structures [8] In thesestudies dopant-caused band tailing has the negligible effectson the spectral yield This is in part due to the processwhere the escape of photocarriers over a potential barrier[2] requires optical transitions ending up at the states withthe energies greater than the barrier In addition the effectof the band tailing is insignificant for the GaAs and type-IIsuperlattice absorber For HgCdTe however the Urbach tail[43] is known to significantly distort the absorption edge Asshown in the inset of Figure 6(c) the IP fitting based on PBAagrees well with the experiment for the high-energy range but

fails to explain the spectral yield in the near-threshold regimeOne possible reason could be due to the trivial influence ofthe potential barrier on the escape of photocarriers whichmeans that the spectral yield is mostly determined by theHg078Cd022Te absorber As a consequence band tailingshould be properly considered in order to fit the yield spectra(see the solid line in the inset of Figure 6(c))

In terms of the structure (Figure 6(a)) electrons escapinginto the Hg068Cd032Te layer under a positive bias need toovercome a barrier resulting from the conduction band offset(CBO) between Hg078Cd022Te and Hg068Cd032Te junctionThe IP threshold of this should be different under negativebias where surmounting the barrier is not needed Howeversuch a difference cannot be identified from the spectral yield


CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te

(733120583m Nd = 12 times 1015 cmminus3

(032120583m Nd = 12 times 1015 cmminus3)

)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)


Hg068Cd032Te Hg078Cd022Te

53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)

Figure 6 (a) Schematic of the 119899-type Hg078Cd022TeHg068Cd032Te heterojunction structure (b)The quantum yield spectra at 53 and 78KSpectra measured at positive and negative biases have a similar profile Inset shows the schematic band alight (without considering the spacecharge effect and composition grading at the junction interface) and the dominant optical transition which occurs in Hg078Cd022Te (c) Thequantum yield spectra at 06 V along with IP fittings (solid line) Inset comparison of fittings using different energy distribution functionswhere 1205881 is an exponential function while 1205882 represents PBA approximation

as shown in Figure 6(b) Both under positive and nega-tive biases display similar spectral profile and no apparentshifting in the thresholds can be observed This confirmsthe negligible electron barrier at the 119899-type Hg068Cd032Te(032 120583m)Hg078Cd022Te (733 120583m) heterojunction interface

3 IP-Based Photodetectors

31 Split-Off Band Heterojunction Infrared Detectors The useof119901-type split-off transition is promising to develop photode-tectors avoiding operation under cryogenic cooling condi-tions Uncooled 119901-GaAsAl119909Ga1minus119909As split-off detectors withhighly doped emitters were demonstrated operating throughthe IP mode [11] The split-off transition corresponds to hole

transitions between the lightheavy-hole bands (LHHH) andthe spin-orbit split-off (SO) band [11 44] The transitionenergy and spectral response range thus depend on the SO-HH splitting energy The photocarriers then escape over theAlGaAs barrier through an internal photoemission processThe room-temperature response [11] of a split-off detector(SP003) is shown in Figure 7(a) This detector contains 30periods of 3 times 1018 cmminus3 119901-doped 188 nm GaAs and 60 nmundoped Al057Ga047As The active region is sandwichedbetween two 119901-type GaAs layers doped to 1 times 1019 cmminus3 Theobtained responsivity is 029mAW and the correspondingdetectivity 119863lowast is 68 times 10

5 Jones at 25 120583m and at roomtemperature


0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)

Figure 7 (a) The experimental and model response [10] for detector sample SP003 at different biases and 300K due to the hole transitionfrom heavy-hole (hh) to spin-orbit split-off (so) bands Both direct (sim27 120583m) and indirect (sim325 120583m) transition peaks were observed (b)The80K responsivity spectra of SP001 at different biases The light-hole (lh) and heavy-hole (hh) transition contribute to the long-wavelengthregion (gt4120583m) A comparison of experiment withmodel free-carrier indirect responsivity (dashed line) for bias at 02 V is shown in the insetindicating the lh-hh response superimposed on the free-carrier response

In addition to the above split-offmechanism the LH-HHtransition is the main contribution to the long-wavelengthspectral response (4ndash10 120583m) This is observed on a 119901-GaAsAl028Ga072As heterostructure (SP001) [12] as shownin Figure 7(b) demonstrating the response up to 165 120583m attemperatures up to 330K [12]

32 Wavelength-Extended Photovoltaic Infrared Photode-tectors Photovoltaic detectors are attractive for achieving(i) extremely low noise (ii) high impedance and (iii) lowpower dissipation compared to photoconductive detectors[45] Various device concepts based on 119901-119899 junctions [46]quantum well (QW) [47] quantum dot (QD) [48 49] type-II InAsGaSb [50] and quantum cascade (QCD) structures[49 51] have been explored to implement photovoltaic oper-ation One of the key factors is to have a built-in potentialto sweep out the photocarriers without using an externalelectric field Schneider et al [47] reported a four-zone lownoise photovoltaic QW infrared photodetector (QWIP) withthe preferable transport of carriers toward one directionwhile internal electric field is associated with the junctionfor a 119899-119894-119901 type-II InAsGaSbAlSb detector [50] RecentlyBarve and Krishna [49] reported a photovoltaic QD infraredphotodetector (QDIP) based on the QCD concept [51] inwhich directional transfer of carriers between QDs is favoredby cascade transitions through phonon coupling

The present PV detector architecture uses the standardstructure of internal photoemission detectors [12] in whicha highly 119901-type doped GaAs acts as the photon absorberand emitter Figure 8(a) shows the valence band which has anonsymmetrical band configuration In addition to an offset

(120575119864V) between the barriers below and above the emitter oneof the AlGaAs barriers is graded to further increase the non-symmetry and facilitate the transport of photoexcited holesat zero bias The room-temperature photovoltaic operationhas been reported elsewhere [52] For comparison differentgradients of Al fractions (ie 119909 varies from 045 to 075 orremains a constant (Table 2)) were investigated Figure 8(b)schematically shows the intervalence band (IVB) transi-tions mainly responsible for photon absorption and holeescape over the barrier (through internal photoemission)To determine 119864119860 the characteristics of dark current-voltage-temperature (I-V-T) were measured (Figure 9(a)) 1198770119860 val-ues extracted from I-V-T data are shown in Figure 9(b)where a previous symmetrical GaAsAl057Ga043As detector(sample SP3) [11] is also shown for comparison The Arrhe-nius plots are used to fit 1198770119860 and determine 119864119860 to be 037040 and 049 eV for samples SP1005 SP1007 and SP1001respectively Except for SP1001 the obtained 119864119860 values arecomparable to the designed internal work function (Δ) ofsim040 eV in accordance with the 119901-type GaAsAl075Ga025Asjunction by taking into account 119901-type-doping effects [2]The 1198770119860-119879 characteristic giving 119864119860 sim 04 eV demonstratedthat both SP1005 and SP1007 behave like a 3 120583m thresholddetector

The figure of merits for the photovoltaic operation isshown in Figures 10(a) and 10(b)119863lowast was obtained [50] usingthe formula 119863lowast = R(2119902119869 + 4119896119879119877diff119860)

12 in which Ris the responsivity 119869 is the dark current density and 119877diffis the differential resistance At zero bias where the shotnoise vanishes this expression is reduced to the normalform in terms of the Johnson noise [48] With decreasing


Table 2 GaAsAl119909Ga1minus119909As photovoltaic detector parameters The active region consists of a 400 nm thick undoped Al1199093Ga1minus1199093As barrierwith constant 1199093 a 119901-type GaAs layer (emitter) doped to 1 times 1019 cmminus3 and a flat (SP1001) or graded (SP1005 and SP1007) 80 nm thickAl119909Ga1minus119909As barrier (119909 varies from 1199092 to 1199091) Figure 8(a) shows the valence band diagram 119889119890 119864119860 and 120582119879 denote the thickness of emitteractivation energy and the threshold wavelength of photovoltaic response respectively

Sample number 1199091 1199092 1199093 119889119890 (nm) 119864119860 (eV) 120582119879 (120583m)SP1001 (flat-barrier) 075 075 057 80 049 39SP1005 (graded-barrier) 045 075 057 20 037 80SP1007 (graded-barrier) 045 075 057 80 040 80

Emitter80nm 400nm TCBC Ef

120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)

Figure 8 (a) The valence band diagram of a graded (solid line)flat (dashed line) barrier structure Bidirectional photocurrents cansimultaneously exist in the sample for photovoltaic operation as shown by 119868119891(+) and 119868119903(minus) corresponding to forward and reversephotocurrents respectively 1199091 1199092 and 1199093 are the Al fractions of the barriers as described in Table 2 120575119864V is an offset between the barriersbelow and above the emitter (b) Schematic of optical transitions between two valence bands that is the heavy-hole (hh) and light-hole (lh)bands For holes to escape over a potential barrier optical transitions typically occur with the assistance of phonons

temperature 119877diff rapidly increases for the bias around 0VTo calculate photovoltaic 119863lowast at 80K extrapolation of 1198770 interms of the Arrhenius plots (Figure 9(b)) has been carriedout

The spectral response of the graded-barrier samplescontains a feature that is the large redshift in the thresh-old wavelength under photovoltaic operation (doubling theoperating wavelength range) From the photoresponse char-acteristic point of view the device with 119864119860 sim 040 eV actsas an 8120583m threshold detector Notice that the flat-barriersample SP1001 does not respond beyond 39 120583m which issimilar to the symmetrical GaAsAl057Ga043As detector asobserved before (sample SP3) [11] Another feature beingobserved is the zero-responsivity point lying between 34and 35 120583m which is an indication of bidirectional photocur-rents simultaneously existing in the sample (see Figure 8(a))This can be understood since photoexcited holes in theemitter can emit over both sides of the barriers whichnormally have the threshold wavelengths of 3 and 4 120583ms

corresponding to the heterointerfaces of GaAsAl075Ga025AsandGaAsAl057Ga043As respectivelyThephotocurrent can-cellation leads to the occurrence of zero response between3 and 4 120583ms Several zero-response points taking place insample SP1001 are related to its band alignment

In general threshold redshiftingmostly results from bias-related effects such as image-force barrier lowering andquantum tunneling However these effects are absent in thephotovoltaic operating mode A testimony of our observa-tions was justified as being due to the high-energy photonexcitation Since the bottom contact (BC) emitter and topcontact (TC) are highly doped photoexcited holes can becreated in all of these layers Because of the graded-barrierhigh-energy photons can give rise to a net flow of photoex-cited holes from BC to emitter Some of the photoexcitedholes are captured by the emitterThese high-energy capturedholes tend to increase the energies of holes [10] originallyin the emitter and excite them to high-energy states As aconsequence the energies of photons needed in order to


Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007

SP3 (reference [19])

300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)

Figure 9 (a) Dark 119868-119881 characteristics at different temperatures (b) The Arrhenius plots of 1198770119860 against 1000119879 to determine the activationenergies (119864119860) All of data result from measurements of 400 times 400 120583m2 mesas except for SP1005 for which an additional device with thedimension of 800 times 800 120583m2 (open circles) is plotted to confirm the consistency Also shown is a previously reported [11] symmetrical flat-barrier detector (SP3) which has the zero barrier offset that is 120575119864V = 0 eV Its 119864119860 corresponds to the activation energy of the 119901-type GaAs(3 times 1018 cmminus3)Al057Ga043As junction

SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005

Reference [17] (photoconductive)

1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2

Wavelength (120583m)2 4 6 8

80K (photovoltaic)

(b)

Figure 10 The spectral (a) responsivity and (b) detectivity at 80K The vertical arrows indicate the occurrence of zero response due tobidirectional photocurrents simultaneously existing in the device owing to the photovoltaic operating mode Labeled responses (1) and (2)correspond to the forward [119868119891(+)] and reverse [119868119903(minus)] photocurrents Long-wavelength response beyond 39 120583m was not observed in flat-barrier sample SP1001 Table 2 summarizes the threshold wavelengths of photovoltaic response for three samples The 119863lowast value of SP1007 is105 times higher than 30-period photoconductive detectors previously reported [12]


Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)

100 of incident light73 of incident light

29 of incident light

Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)

Figure 11 (a) Photovoltaic response measured by using different long-pass filters (120582CO is the cut-on wavelength) A filter with 120582CO = 360 120583mblocks the transport of photoexcited holes overcoming the graded-barrier region thus suppressing both the short- and long-wavelengthresponse (b) Variation of photovoltaic response with the intensities of incident light (through adjusting the optical aperture size of thespectrometer) where 100 of light corresponds to the default aperture sizeThe calibration of responsivity takes into account the variation oflight which leads to nearly unchanged responsivity values for the lt3 120583mwavelength rangeThe gt35 120583m response becomes almost negligiblewhen the intensity of incoming light is reduced to 29

excite holes to escape over the barrier can be correspondinglyreduced giving rise to a long-wavelength response Thisprocess takes place in the hole transport from BC to TCin agreement with observed wavelength-extended responsecorresponding to the reverse photocurrents (Figure 10)

To justify the above mechanism spectral response hasbeen measured with the use of different long-pass filters(with the cut-on wavelength of 120582CO) and different intensitiesof incoming light as shown in Figure 11 This varies theenergy or the concentration of photoexcited holes injectedinto the emitter By using a filter with 120582CO = 360 120583m theshort-wavelength response (labeled region 1 of Figure 10)should disappear as the escape of holes from the emitter tothe BC cannot be accomplished because of the missing of theℎ] gt 034 eV (120582 lt 360 120583m) photons For the same reasonphotoexcited holes in the BC will be unable to overcomethe graded-barrier (highest barrier sim 04 eV) to enter intoemitter This suppresses the long-wavelength response aswell (labeled region 2 of Figure 10) according to the afore-mentioned energy transfer mechanism As expected(Figure 11(a)) photovoltaic response was unseen throughoutthe entire spectral range In contrast the use of a filter with120582CO = 240 120583m gives rise to both short- and long-wavelengthresponse owing to allowed emitter-to-BC and BC-to-emitter

hole transport The efficiency of energy transfer betweenphotoexcited holes and holes in the emitter could be a criticalfactor determining the long-wavelength response Suchenergy transfer results from carrier scatterings and could besubject to degradation from hole-impurity scattering as theemitter is highly doped With increasing the concentrationof photoexcited holes enhanced hole-hole scatterings canbe expected leading to distinct response in long-wavelengthrange (Figure 11(b)) By taking into account the intensityof the incoming light the short-wavelength portion of theresponse is expected to remain the same However thelong-wavelength portion is almost negligible when the lightintensity is reduced to 29 and quickly rises up whenthe incoming light increases to 73 where 100 of lightcorresponds to the default optical aperture in the experimentThis may also explain the response characteristic of sampleSP1001 not beyond 39 120583m where because of the flat-barrierconfiguration the net injection of photoexcited holes fromthe BC to emitter is negligible

Higher activation energy of the dark current-voltagecharacteristics than the photoresponse threshold energy canprovide a significant improvement of the detector perfor-mance According to 1198770119860 sim exp(minus119864119860119896119879) the 1198770119860 value (at80K) of our detector with 119864119860 = 040 eV (responding up to


Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector

Semi-insulating GaAs substrate

(700nm)

(100nm)

AlxGa1minusxAs (80nm)

V

Al057Ga043As (400nm)

p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)

CollectorAbsorberInjector

Gradedbarrier barrier

Constant0V

Negativebias

With hot-hole effect

120575E

120575E

Alx1Ga1minusx1AsAlx2Ga1minusx2As

Alx3Ga1minusx3As

(b)

Figure 12 (a) The structure of the 119901-type GaAsAl119909Ga1minus119909As hot-hole photodetector Graded-barrier Al fractions vary from 1199091 to 1199092 whilethe constant barrier Al fraction is 1199093 (b) Schematic of the valence band alignment (including band bending) The offset between the barriersbelow and above the 119901-GaAs absorber is labeled as 120575119864V

0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007

0 04 08Bias voltage (V)

(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)

Experiment (minus006V)Experiment (minus012V)Model (Δ998400 = 0012 eV)

(at minus012V)

dSW

pum

p dF

Figure 13 Measured photoresponse at 53 K and the fittings based on the escape-cone model The fittings give a reduced threshold energyat Δ1015840 = 0012 eV The vertical arrows indicate the GaAs and AlAs-like phonons Inset differential SWpump

8 120583m) is nearly 1015 times higher than a conventional detectorwith 119864119860 of 0155 eV (without wavelength extension alsoresponding up to 8 120583m) which gives nearly 107 improvementin 119863lowast To experimentally evaluate the 119863lowast improvement

factor same type of internal photoemission detectors [12] wascompared as shown in Figure 10(b) (this detector contains 30periods of emitters and barriers) which is nearly 105 timesless than the present detector

33 Hot-Hole Photodetectors with aResponse Beyond the BandGap Spectral Limit A novel concept of photodetection isdeveloped based on an energy transfer process between hotand cold carriers enabling spectral extension in surpassingthe standard limit set by 120582119888 = ℎ119888Δ [14] (120582119888 is the thresholdwavelength and Δ is the activation energy) The principle is

associated with the excitation of cold holes into higher energystates by interacting with hot holes and thus the respondingof these high-energy carriers to the long-wavelength infraredradiation

The 119901-type samples GaAsAl119909Ga1minus119909As were used todemonstrate hot-hole response As shown in Figure 12(a)these samples contain119901-type doped (1times1019 cmminus3) GaAs lay-ers they are the injector absorber and collector respectivelyThe VB alignment is schematically plotted in Figure 12(b)By absorbing photons the holes in the injector are excitedand injected into the absorber After passing over the barrierthese holes have high energies and thus are ldquohotrdquo comparedto the original holes in the absorber [53]

Photoresponse was measured at 53 K as plotted inFigure 13 which shows a very long-wavelength infrared


Long-passfilter

Semi-insulatingGaAs beamsplitter

FTIR

DetectorsampleOptical

excitation source

Figure 14 Experimental apparatus where the double-side polished semi-insulating GaAs wafer acts as a beamsplitter

(VLWIR) response In terms of the internal work function(ie Δ) [2] of the absorberconstant barrier junction (Δ =

032 eV) the designed limit should be only 39120583m (shadedregion) As shown in Figure 13 the VLWIR response can beexplained by a fitting [54] using the value Δ = 0012 eV

The hot-cold carrier energy transfer mechanism is inpart supported by the differential photocurrent The short-wavelength light in the measurement (eg from the Fouriertransform infrared (FTIR) spectrometer) is denoted as theldquopumprdquo The pump light is responsible for the generation ofhot holes which can be described using a three-dimensionaldrift model [45]

119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)

where 119868puph represents the pump current and 119873(120598) is the holeconcentration [55] Taking the derivative of 119868puph with respectto 119865 gives

119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)

in which the image-force barrier lowering and the tilting ofthe graded-barrier under the field have a primary effect on119889Δ119889119865 [2] For the high-field region the first term of (7) isnegligible The differential 119868puph thus determines the energydistribution of holes 119868puph can be evaluated as being pro-portional to the spectral weight (SW) of the response definedas

SW prop int

120582max

120582min

R (120582) 119889120582 (8)

whereR(120582) is the spectral responsivityThe inset of Figure 10shows three peaks at minus012 minus040 and 010V As a com-parison another sample which does not display the VLWIRresponse peaks only displays one differential SW peak at 0VThe previous studies using hot-carrier spectroscopy [55 56]indicate that the distribution peaks are the sign of the hot-cold carrier interaction

The VLWIR response as a consequence of the hot-cold carrier energy transfer indicates that the response canbe tuned by varying the degree of the hot-hole injectionFigure 14 plots the experimental setup A long-pass filterwith the cut-on wavelength 120582CO = 45 120583m (corresponding

to 028 eV) is used to block the high-energy (gt028 eV)photons (from spectrometer) The hot holes are provided byphotoexcitation using an external high-energy light Figure 15shows the photocurrent (spectral weight of the response) atdifferent excitation levels The result indicates that increasingthe excitation intensity enables the VLWIR response

In summary we presented IP studies on InAsGaSbT2SL and HgCdTe photodetectors The band gaps of photonabsorbers and their temperature dependence are determinedby IP spectroscopy based on fittings to the quantum yieldnear-threshold regimesWe also demonstrated an IP detectorwith extended response up to 55120583m The tunability of theresponse is demonstrated by varying the degree of the hot-hole injection

4 Outlook of the IP Methodology

Thegeneric characteristics of IP is associated with the processof generation and emission of photocarriers IP exists in avariety of optical processes including the bulk [57] quantum[58] and even semiconductor-liquid electrolyte junctions[59] The IP signal can be detected through an electric field[57] a second photon [60] or second-harmonic generation[61]Therefore IP can be applied to a large extent of materialsand heterojunction The variation in the way of detectingthe signal will also enable studying different properties thanthose that have been reviewed in this paper for example thecarrier-carrierphonon scatterings

This review has focused on the IP phenomena in theinfrared wavelength range which typically corresponds tothe energy of photon less than the value of the band gap Amore comprehensive review of IP on studying optical processacross the band gap and in the wide-band gap materials canbe found in [1]

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported in part by the US Army ResearchOffice under Grant no W911NF-15-1-0018 monitored by DrWilliam W Clark and in part by the US National ScienceFoundation under Grant no ECCS-1232184


0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)

of long-pass filter2 times TO(X) phonon

of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1

Figure 15 (a) Spectral weights of response Different excitation levels are indicated as119875ext-1ndash119875ext-8The sample undermeasurements is SP1006(b) Power of the external excitation optical source (incident on the active area of 260 times 260 120583m2) (c)-(d) The VLWIR response (at minus01V)varying with the excitation power The arrows indicate the cut-on wavelength of the filter and the 2 times TO(119883) phonon features of the GaAsbeamsplitter respectively

References

[1] V Afanasrsquoev Internal Photoemission Spectroscopy Principles andApplications Elsevier Science 2010

[2] Y-F Lao and A G U Perera ldquoTemperature-dependent internalphotoemission probe for band parametersrdquo Physical Review Bvol 86 no 19 Article ID 195315 9 pages 2012

[3] R Yan Q ZhangW Li et al ldquoDetermination of graphene workfunction and graphene-insulator-semiconductor band align-ment by internal photoemission spectroscopyrdquo Applied PhysicsLetters vol 101 no 2 Article ID 022105 2012

[4] Y Hikita M Kawamura C Bell and H Y Hwang ldquoElectricfield penetration in AuNbSrTiO3 Schottky junctions probedby bias-dependent internal photoemissionrdquo Applied PhysicsLetters vol 98 no 19 Article ID 192103 2011

[5] J Batey and S L Wright ldquoEnergy band alignment inGaAs(AlGa)As heterostructures the dependence on alloycompositionrdquo Journal of Applied Physics vol 59 no 1 pp 200ndash209 1986

[6] T B Bahder ldquoEight-band ksdotp model of strained zinc-blendecrystalsrdquo Physical Review B vol 41 no 17 pp 11992ndash12001 1990

[7] P Lautenschlager M Garriga S Logothetidis andM CardonaldquoInterband critical points of GaAs and their temperature depen-dencerdquo Physical Review B vol 35 no 17 pp 9174ndash9189 1987

[8] Y-F Lao P K D D P Pitigala A G Unil Perera E PlisS S Krishna and P S Wijewarnasuriya ldquoBand offsets andcarrier dynamics of type-II InAsGaSb superlattice photodetec-tors studied by internal photoemission spectroscopyrdquo AppliedPhysics Letters vol 103 no 18 Article ID 181110 2013

[9] Y-F Lao A G U Perera L H Li S P Khanna E H Linfieldand H C Liu ldquoTunable hot-carrier photodetection beyond thebandgap spectral limitrdquo Nature Photonics vol 8 no 5 pp 412ndash418 2014

[10] S G Matsik P V V Jayaweera A G U Perera K K Choiand P Wijewarnasuriya ldquoDevice modeling for split-off banddetectorsrdquo Journal of Applied Physics vol 106 no 6 Article ID064503 2009

[11] P V V Jayaweera S G Matsik A G U Perera H C Liu MBuchanan and Z R Wasilewski ldquoUncooled infrared detectorsfor 3ndash5 120583m and beyondrdquo Applied Physics Letters vol 93 no 2Article ID 021105 2008

[12] Y F Lao P K D D P Pitigala A G U Perera et al ldquoLight-hole and heavy-hole transitions for high-temperature long-wavelength infrared detectionrdquo Applied Physics Letters vol 97no 9 Article ID 091104 2010

[13] R H Fowler ldquoThe analysis of photoelectric sensitivity curvesfor clean metals at various temperaturesrdquo Physical Review vol38 no 1 pp 45ndash56 1931


[14] S M Sze and K K Ng Physics of Semiconductor Devices JohnWiley amp Sons New York NY USA 2007

[15] C Coluzza E Tuncel J-L Staehli et al ldquoInterface measure-ments of heterojunction band lineups with the Vanderbilt free-electron laserrdquo Physical Review B vol 46 no 19 pp 12834ndash12836 1992

[16] C Caroli J S Helman and F S Sinencio ldquoInternal photoe-mission of holes from a semiconductor into a semiconductorrdquoPhysical Review B vol 11 no 2 article 980 1975

[17] E O Kane ldquoTheory of photoelectric emission from semicon-ductorsrdquo Physical Review vol 127 no 1 pp 131ndash141 1962

[18] W Seidel O Krebs P Voisin J C Harmand F Aristone and JF Palmier ldquoBand discontinuities in In119909 Ga1minus119909 As-InP and InP-Al119910 In1minus119910 as heterostructures evidence of noncommutativityrdquoPhysical Review B vol 55 no 4 pp 2274ndash2279 1997

[19] V V Afanasrsquoev and A Stesmans ldquoInternal photoemissionat interfaces of high-120581 insulators with semiconductors andmetalsrdquo Journal of Applied Physics vol 102 no 8 Article ID081301 28 pages 2007

[20] R Williams ldquoInjection phenomenardquo in Semiconductors andSemimetals R Willardson and A Beer Eds chapter 2 Aca-demic Press New York NY USA 1970

[21] A M Goodman ldquoPhotoemission of electrons from n-typedegenerate silicon into silicon dioxiderdquoPhysical Review vol 152no 2 pp 785ndash787 1966

[22] R J Powell ldquoInterface barrier energy determination from volt-age dependence of photoinjected currentsrdquo Journal of AppliedPhysics vol 41 no 6 pp 2424ndash2432 1970

[23] E O Kane ldquoThomas-fermi approach to impure semiconductorband structurerdquo Physical Review vol 131 no 1 pp 79ndash88 1963

[24] J Noffsinger E Kioupakis C G Van de Walle S G LouieandM L Cohen ldquoPhonon-assisted optical absorption in siliconfrom first principlesrdquo Physical Review Letters vol 108 no 16Article ID 167402 2012

[25] A Frova and P Handler ldquoDirect observation of phonons insilicon by electric-field-modulated optical absorptionrdquo PhysicalReview Letters vol 14 no 6 pp 178ndash180 1965

[26] R Newman and W W Tyler ldquoEffect of impurities on free-holeinfrared absorption in p-type germaniumrdquo Physical Review vol105 no 3 pp 885ndash886 1957

[27] R Braunstein and L Magid ldquoOptical absorption in p-typegallium arseniderdquo Physical Review vol 111 no 2 pp 480ndash4811958

[28] M Cardona K L Shaklee and F H Pollak ldquoElectroreflectanceat a semiconductor-electrolyte interfacerdquo Physical Review vol154 no 3 article 696 1967

[29] M Munoz K Wei F H Pollak J L Freeouf and G WCharache ldquoSpectral ellipsometry of GaSb experiment andmodelingrdquo Physical Review B vol 60 no 11 pp 8105ndash8110 1999

[30] A G Thompson M Cardona K L Shaklee and J C WoolleyldquoElectroreflectance in the GaAs-GaP alloysrdquo Physical Reviewvol 146 no 2 pp 601ndash610 1966

[31] I Vurgaftman J R Meyer and L R Ram-Mohan ldquoBand para-meters for III-V compound semiconductors and their alloysrdquoJournal of Applied Physics vol 89 no 11 pp 5815ndash5875 2001

[32] J S Blakemore ldquoSemiconducting and other major properties ofgallium arseniderdquo Journal of Applied Physics vol 53 no 10 ppR123ndashR181 1982

[33] E O Kane ldquoEnergy band structure in p-type germanium andsiliconrdquo Journal of Physics and Chemistry of Solids vol 1 no 1-2pp 82ndash99 1956

[34] M Kuball M K Kelly M Cardona K Kohler and J WagnerldquoDoping dependence of the 1198641 and 1198641+Δ 1 critical points inhighly doped n- and p-type GaAs importance of surface bandbending and depletionrdquo Physical Review B vol 49 no 23 pp16569ndash16574 1994

[35] M Heiblum D Galbi and M Weckwerth ldquoObservation ofsingle-optical-phonon emissionrdquo Physical Review Letters vol62 no 9 article 1057 1989

[36] Q O Hu E S Garlid P A Crowell and C J PalmstroslashmldquoSpin accumulation near FeGaAs (001) interfaces the role ofsemiconductor band structurerdquo Physical Review B vol 84 no8 Article ID 085306 5 pages 2011

[37] DC Tsui ldquoEvidence forHole-To-Phonon interaction from tun-neling measurements in GaAs-Pb junctionsrdquo Physical ReviewLetters vol 21 no 14 pp 994ndash996 1968

[38] J L T Waugh and G Dolling ldquoCrystal dynamics of galliumarseniderdquo Physical Review vol 132 no 6 pp 2410ndash2412 1963

[39] P Giannozzi S deGironcoli P Pavone and S Baroni ldquoAb initiocalculation of phonon dispersions in semiconductorsrdquo PhysicalReview B vol 43 no 9 pp 7231ndash7242 1991

[40] S Steiger M Salmani-Jelodar D Areshkin et al ldquoEnhancedvalence force field model for the lattice properties of galliumarseniderdquo Physical Review BmdashCondensed Matter and MaterialsPhysics vol 84 no 15 Article ID 155204 2011

[41] E A Plis S S Krishna N Gautam S Myers and S KrishnaldquoBias switchable dual-band InAsGaSb superlattice detectorwith pBp architecturerdquo IEEE Photonics Journal vol 3 no 2 pp234ndash240 2011

[42] J P Laurenti J Camassel A Bouhemadou B Toulouse RLegros and A Lusson ldquoTemperature dependence of the funda-mental absorption edge of mercury cadmium telluriderdquo Journalof Applied Physics vol 67 no 10 pp 6454ndash6460 1990

[43] F Urbach ldquoThe long-wavelength edge of photographic sensitiv-ity and of the electronic absorption of solidsrdquo Physical Reviewvol 92 no 5 p 1324 1953

[44] A G U Perera ldquoQuantum structures for multiband photondetectionrdquo Opto-Electronics Review vol 14 no 2 pp 103ndash1122006

[45] H Schneider and H C Liu Quantum Well Infrared Photode-tectors Physics and Applications vol 126 of Springer Series inOptical Sciences Springer New York NY USA 2007

[46] A Rogalski ldquoHeterostructure infrared photovoltaic detectorsrdquoInfrared Physics amp Technology vol 41 no 4 pp 213ndash238 2000

[47] H Schneider C Schonbein M Walther K Schwarz J Fleiss-ner and P Koidl ldquoPhotovoltaic quantumwell infrared photode-tectors the four-zone schemerdquo Applied Physics Letters vol 71no 2 pp 246ndash248 1997

[48] L Nevou V Liverini F Castellano A Bismuto and J FaistldquoAsymmetric heterostructure for photovoltaic InAs quantumdot infrared photodetectorrdquo Applied Physics Letters vol 97 no2 Article ID 023505 2010

[49] AV Barve and SKrishna ldquoPhotovoltaic quantumdot quantumcascade infrared photodetectorrdquo Applied Physics Letters vol100 no 2 p 021105 2012

[50] A M Hoang G Chen A Haddadi S Abdollahi Pour and MRazeghi ldquoDemonstration of shortwavelength infrared photodi-odes based on type-II InAsGaSbAlSb superlatticesrdquo AppliedPhysics Letters vol 100 no 21 Article ID 211101 2012

[51] F R Giorgetta E Baumann M Graf et al ldquoQuantum cascadedetectorsrdquo IEEE Journal of Quantum Electronics vol 45 no 8pp 1039ndash1052 2009


[52] P K D D P Pitigala S G Matsik A G U Perera et alldquoPhotovoltaic infrared detection with p-type graded barrierheterostructuresrdquo Journal of Applied Physics vol 111 no 8Article ID 084505 2012

[53] F Capasso ldquoBand-gap engineering from physics and materialsto new semiconductor devicesrdquo Science vol 235 no 4785 pp172ndash176 1987

[54] D G Esaev M B M Rinzan S G Matsik and A G U PereraldquoDesign and optimization of GaAsAlGaAs heterojunctioninfrared detectorsrdquo Journal of Applied Physics vol 96 no 8 pp4588ndash4597 2004

[55] J R Hayes A F J Levi and W Wiegmann ldquoHot-electronspectroscopy of GaAsrdquo Physical Review Letters vol 54 no 14article 1570 1985

[56] A F J Levi J R Hayes P M Platzman and W WiegmannldquoInjected-hot-electron transport in GaAsrdquo Physical ReviewLetters vol 55 no 19 pp 2071ndash2073 1985

[57] A BraunsteinM BraunsteinG S Picus andCAMead ldquoPho-toemissive determination of barrier shape in tunnel junctionsrdquoPhysical Review Letters vol 14 no 7 pp 219ndash221 1965

[58] A Prem and V V Kresin ldquoPhotoionization profiles of metalclusters and the Fowler formulardquo Physical Review A vol 85 no2 Article ID 025201 4 pages 2012

[59] FWilliams andA J Nozik ldquoSolid-state perspectives of the pho-toelectrochemistry of semiconductorndashelectrolyte junctionsrdquoNature vol 312 no 5989 pp 21ndash27 1984

[60] M Cinchetti K Heimer J-P Wustenberg et al ldquoDetermina-tion of spin injection and transport in a ferromagnetorganicsemiconductor heterojunction by two-photon photoemissionrdquoNature Materials vol 8 no 2 pp 115ndash119 2009

[61] WWang G Lupke M Di Ventra et al ldquoCoupled electron-holedynamics at the SiSiO2 interfacerdquo Physical Review Letters vol81 no 19 pp 4224ndash4227 1998

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



(1) (2)

Emitter

hh

hh

lh

lhBarrier

(ii) (i)

(1)(2)VB

Ef

Ef

p-emitter i-barrier

120588(120598 minusEf) middot f(120598)

(a)

PBAwithout tail

PBA with aGaussian tail

DOS DOS

Ener

gy

EfEf

(b)

Figure 1 (a) Schematic band diagram of a 119901-emitter119894-barrier structure 120588(120598 minus119864119891)119891(120598) is the multiplication of the energy distribution (120588)and the FD function (119891) (i) and (ii) correspond to the nondegenerate and degenerate doping respectively IP processes labeled as (1) and(2) consist of optical transitions in the emitter and the escaping of holes from the emitter to the barrier (b) DOS with and without the bandtailing effect

that this occurs at the above-threshold regime and afterexcitation the excess kinetic energy of carriers should begreater than the phonon energy Upon scatterings a portionof photocarriers could remain in the absorber unable toescape which leads to degradation in the photoresponse Adetailed study on this should benefit future improvementof the device performance The IP approach studying thescattering effects has been recently demonstrated [8] throughfitting of the near-threshold quantum yield spectra

In an IP experiment photoemitted carriers are col-lected and detected as a photocurrent varying with thephoton energy The IP effect for photodetection requiresthe use of a heterostructure An important concept recentlydemonstrated [9] is the photoresponse extension triggeredby introducing a hot-cold carrier energy mechanism Thephotoresponse is substantially extended without the need ofreducing the IP threshold energy

In this review we discuss the IP spectroscopy as amethodto characterize semiconductors and heterostructures and usethe IP effect to develop photodetectors

2 IP Characterization of Band Parameters

21 TheTheory of the IP Spectroscopy The theoretical basis ofIP was initially reported in Fowlerrsquos works [13] on externalphotoemission of electrons (from metal to vacuum) Theoriginal form of the quantum yield 119884 can be expressed as

119884 sim 119891 (120583) sdot (119896119879)2 (1)

which contains a 119879-dependent term 119891(120583) has the followingexpression [13]119891 (120583)

=

119890120583minus1198902120583

4+1198903120583

9minus sdot sdot sdot (120583 ⩽ 0)

1205872

6+1205832

2minus (119890minus120583minus119890minus2120583

4+119890minus3120583

9minus sdot sdot sdot ) (120583 ⩾ 0)

(2)

where 120583 equiv (ℎ] minus Δ)119896119879 and ℎ] is the photon energy Fowlerrsquosyield function can be actually reduced [14] to be independentof 119879 when ℎ] gt Δ + 3119896119879 that is

119884 (ℎ]) sim (ℎ] minus Δ)2 (3)

Fowlerrsquos yield function is mainly used to fit the IP thresholdsDespite the fact that Fowlerrsquos yield function was originallyderived for external photoemission it has been applied [15]to many IP cases By taking into account the fact thatsemiconductors have a different band structure compared tometal exponent ldquo2rdquo in (3) is replaced with a parameter 119901 [16ndash19]The value of 119901was reported varying between 1 and 3 [19]By taking 119901 as a fitting parameter the physical meaning ofthe yield function becomes unclear Furthermore the effectof the temperature on the IP process is ignored which couldcause underestimate of Δ This result is significant when theyield function applied to the low-energy limit for example inthe energy range of lt1 eV

To obtain accurate IP thresholds temperature-dependentIP spectroscopy (TDIPS) has been developed Figure 1(a)shows the TDIPS principle for a 119901-type structure whichincludes two doping concentrations under which 119864119891 can befound to be (i) above and (ii) below the top of the valenceband (VB) By absorbing photons photoexcited holes withhigh energies from the emitter escape over the potentialbarrier The photoemission process of carrier transport fromthe emitter to the barrier is shown in the inset of Figure 1(a)During this process there exist photon absorption and scat-terings The scattering is crucial for the photoexcited holesto be transferred across the emitter-barrier interface Bothdirect and indirect transitions can lead to photoexcitation andhave the primary contributions to the IP yield in the energyregime near and greater than the IP threshold respectively

To obtain the band offsets the line shape of the spectralquantum yield should be considered It should be noted thatthe IP yield concerns with the primary processes includingthe carriersrsquo energies and the escape probabilities of thesecarriers which can be evaluated by considering the photoex-citation of holes via intervalence band (IVB) transitions [12](120588(120598 ℎ]minus119864119891)) and the escape of the holes (119875(120598 Δ)) [20]Theseconsiderations lead to the following expression119884 (ℎ]) = 1198840 (119896119879)

+ 1198620 int

infin

Δ119891 (120598 ℎ]) 120588 (120598 ℎ] minus 119864119891) 119875 (120598 Δ) 119889120598

(4)

where 120588(120598 ℎ] minus 119864119891) is an energy distribution function and119875(120598 Δ) a probability function1198620 is a constant 120598 is the energy










1198892119884

119889 (ℎ])2sim119889 (JDOS)119889 (ℎ])

(5)









PhononEn

ergy

Band edge

HH

LH

SO

(1)

(2)

(3) (4)

(5)

Ef

EfEB

EB

B

BE

ℏ1205962

ℏ1205961

ℏ1205963

ℏ1205964

111⟩⟩k 100⟩⟩k

(a)

12 9

0

5 6 3

p-type GaAs


1 times3 times

120572(103

cmminus1

)1019 cmminus3

1018 cmminus3

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)01 02 03 04 05 06 07

D

A

B

C

D

80KA (6V)

B (6V)

C (6V)

(minus05V)

188nm

188nm

188nm

80nm

015 eV

022 eV

032 eV

032 eV025

eV042

eV

HH rarr LH

HH rarr SO

(c)






Photon energy (eV)03 033 036 039 042 045

Photon energy (eV)

Photon energy (eV)

03 033 036 039 042 045

(a)

(b)

(d)

0008

001

0012

03 033 036 039 042 045

(c)

Sample ABolometer


AD

E

ADE

dYd

(h)

(au

)d2Y

d(h)

2(a

u)

d2Id(h)2

TA(X

)

TA(L

)

TA(L

)

2times

TA(L

)

LO(X

)

LO(Γ

)

3times

TO(Γ

)

Δ0

Δ0

d(JDOS)d(h)

JDO

S (e


log(Y

) (au

)

HH rarr SO VHS

LH rarr SO VHS

inej

]

]Ei(k

)minusEj(k)

1nablaksum

[






50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300



Δ0

(eV

)

(b)







Steiger et ald 332 361 289 89 88





GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation


















1198892119884

119889 (ℎ])2sim119889 (JDOS)119889 (ℎ])

(5)









PhononEn

ergy

Band edge

HH

LH

SO

(1)

(2)

(3) (4)

(5)

Ef

EfEB

EB

B

BE

ℏ1205962

ℏ1205961

ℏ1205963

ℏ1205964

111⟩⟩k 100⟩⟩k

(a)

12 9

0

5 6 3

p-type GaAs


1 times3 times

120572(103

cmminus1

)1019 cmminus3

1018 cmminus3

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)01 02 03 04 05 06 07

D

A

B

C

D

80KA (6V)

B (6V)

C (6V)

(minus05V)

188nm

188nm

188nm

80nm

015 eV

022 eV

032 eV

032 eV025

eV042

eV

HH rarr LH

HH rarr SO

(c)






Photon energy (eV)03 033 036 039 042 045

Photon energy (eV)

Photon energy (eV)

03 033 036 039 042 045

(a)

(b)

(d)

0008

001

0012

03 033 036 039 042 045

(c)

Sample ABolometer


AD

E

ADE

dYd

(h)

(au

)d2Y

d(h)

2(a

u)

d2Id(h)2

TA(X

)

TA(L

)

TA(L

)

2times

TA(L

)

LO(X

)

LO(Γ

)

3times

TO(Γ

)

Δ0

Δ0

d(JDOS)d(h)

JDO

S (e


log(Y

) (au

)

HH rarr SO VHS

LH rarr SO VHS

inej

]

]Ei(k

)minusEj(k)

1nablaksum

[






50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300



Δ0

(eV

)

(b)







Steiger et ald 332 361 289 89 88





GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










PhononEn

ergy

Band edge

HH

LH

SO

(1)

(2)

(3) (4)

(5)

Ef

EfEB

EB

B

BE

ℏ1205962

ℏ1205961

ℏ1205963

ℏ1205964

111⟩⟩k 100⟩⟩k

(a)

12 9

0

5 6 3

p-type GaAs


1 times3 times

120572(103

cmminus1

)1019 cmminus3

1018 cmminus3

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)01 02 03 04 05 06 07

D

A

B

C

D

80KA (6V)

B (6V)

C (6V)

(minus05V)

188nm

188nm

188nm

80nm

015 eV

022 eV

032 eV

032 eV025

eV042

eV

HH rarr LH

HH rarr SO

(c)






Photon energy (eV)03 033 036 039 042 045

Photon energy (eV)

Photon energy (eV)

03 033 036 039 042 045

(a)

(b)

(d)

0008

001

0012

03 033 036 039 042 045

(c)

Sample ABolometer


AD

E

ADE

dYd

(h)

(au

)d2Y

d(h)

2(a

u)

d2Id(h)2

TA(X

)

TA(L

)

TA(L

)

2times

TA(L

)

LO(X

)

LO(Γ

)

3times

TO(Γ

)

Δ0

Δ0

d(JDOS)d(h)

JDO

S (e


log(Y

) (au

)

HH rarr SO VHS

LH rarr SO VHS

inej

]

]Ei(k

)minusEj(k)

1nablaksum

[






50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300



Δ0

(eV

)

(b)







Steiger et ald 332 361 289 89 88





GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Photon energy (eV)03 033 036 039 042 045

Photon energy (eV)

Photon energy (eV)

03 033 036 039 042 045

(a)

(b)

(d)

0008

001

0012

03 033 036 039 042 045

(c)

Sample ABolometer


AD

E

ADE

dYd

(h)

(au

)d2Y

d(h)

2(a

u)

d2Id(h)2

TA(X

)

TA(L

)

TA(L

)

2times

TA(L

)

LO(X

)

LO(Γ

)

3times

TO(Γ

)

Δ0

Δ0

d(JDOS)d(h)

JDO

S (e


log(Y

) (au

)

HH rarr SO VHS

LH rarr SO VHS

inej

]

]Ei(k

)minusEj(k)

1nablaksum

[






50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300



Δ0

(eV

)

(b)







Steiger et ald 332 361 289 89 88





GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











50K

40K

53K

d2Y

d(h)

2(a

u)

Sample D (minus05V)

(a)

0334

0336

0338

034

0342

Temperature (K)0 50 100 150 200 250 300



Δ0

(eV

)

(b)







Steiger et ald 332 361 289 89 88





GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










GaSb Te substrate






(a)

I

I

II

II

III

III

Forwardbias

bias


MWIR

Reverse

(b)

02 04 06 08




01 015 02 025

Qua

ntum

yie

ld (a

u)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)


P(120598 Δ) = 1

P(120598 Δ) = 1

P(120598 Δ) = 1


0228 eVΔ = 0117 eV Δ = 0157 eV

0148 eV

78K

(c)







CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










CdTe passivation

CdTe buffer

Si substrate

078Cd022Te

068Cd032Te



)n-Hg

n-Hg

(a)

Qua

ntum

yie

ld (a

u)



53K

78KCB

VB

(times15)

06Vminus06V

(b)

Qua

ntum

yie

ld (a

u)

Photon energy (eV)

Photon energy (eV)

Yiel

d (a

u)

0055 006 0065

006 008 01 012 014

Fit

53K

(times15)

1205881(E)1205882(E)

Exp (53K)Exp (78K)

(c)








0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0

01

02

03Re

spon

sivity

(mA

W)

2 3 4

Cal Exp

Direct

Indirect


300K

1V2V

3V4V

(a)

Resp

onsiv

ity (m

AW

)

Resp

onsiv

ity (m

AW

)

0

005

01

015

3 6 9 12

Exp

lh-hh(2)lh-hh(1)

so-hh

Cal

0

1

05

15

4 6 12 148 10Wavelength (120583m)


1V

2V

6V

4V

02V

Bias 02V80K

(b)












120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













120575E

x1 x2 x3

If(+)

Ir(minus)

(a)

Ener

gyhh

lh

so

Potentialbarrier

Ef

100⟩⟩k

(b)







Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Voltage (V)4

SP1005

SP1007

SP1001

minus4 minus2 0 2

100

10minus2

10minus4

10minus6Dar

k cu

rren

t den

sity

(Ac

m2 )

80K

220K

180K

(a)

SP1001

SP1005

SP1007


300 250 200 150

100

102

104

106

108

4 5 6 7 8

T (K)

EA = 049 eV

EA = 030 eV

EA = 037 eV

EA = 040 eV

R0A

(Ωcm

2 )

1000T (Kminus1)

(b)


SP1007SP1005

SP1001


Resp

onsiv

ity (A

W)

80K(photovoltaic)

10minus6

10minus7

10minus8

10minus9

1

2

2

4 6 8

(a)

SP1007SP1005


1012

1010

107

Det

ectiv

ity (c

m H

z12

W)

1 2


80K (photovoltaic)

(b)



Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Resp

onsiv

ity (A

W) 10minus7

10minus8

10minus9


120582CO = 240120583m120582CO = 360120583m

(a)



Resp

onsiv

ity (a

u)

10minus7

10minus8


(b)







Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Infrared radiation

TiPtAu

TiPtAu

Collecto

r

Absorber

Injector


(700nm)

(100nm)


V


p+-GaAs

p+-GaAs

absorberp+-GaAs

(a)



Constant0V

Negativebias


120575E

120575E


Alx3Ga1minusx3As

(b)


0

20

40

60

2 4 10 20 30 40 50

GaA

sph

ononAlA

s-lik

eph

onon

SP1007

SP1007


(i)(ii)

(iii)

Experiment53K


Phot

ores

pons

e (120583A

W)

minus08 minus04

(Δ = 032 eV)


(at minus012V)

dSW

pum

p dF









Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Long-passfilter


FTIR


excitation source





119868puph = 119890 sdot V (119865) int

+infin

Δ119873(120598) 119889120598 (6)


119889119868puph

119889119865= 119890 sdot

119889V (119865)119889119865

int

+infin

Δ119873(120598) 119889120598 minus 119890 sdot V (119865)

119889Δ

119889119865sdot 119873 (Δ) (7)


SW prop int

120582max

120582min

R (120582) 119889120582 (8)










Acknowledgments



0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

0

minus05

minus1

Bias

(V)

5 10 15 20Wavelength (120583m)

5 10 15 20Wavelength (120583m)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

0

25

50

(times10minus6)

02 4 6

01

02

03


P ext

(mW

)

(a)

(b)

Pext-6

Pext-6

Pext-5

Pext-5

Pext-4

Pext-4

Pext-3

Pext-3

Pext-2Pext-1

Pext-2Pext-1

Figure 15 Continued


0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0

5

10

5 10 15 20

5 10 15 20



0

0

4

8

01

02

03

P ext

(mW

)

Threshold(c)

(d)


of GaAs

ℛ(120583

AW

)

Pext-6Pext-5Pext-4

Pext-3Pext-2Pext-1


References


































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





























































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









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