research institute for technical physics and materials science of the hungarian academy of sciences...

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences

GaN heterostructures with diamond and graphene for high power applications

B. PéczInstitute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian

Academy of SciencesMTA TTK MFA, 1121 Budapest, Konkoly-Thege M. u. 29-33, Hungary

Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences

High power devices optoelectronicsblue LED---> Nobel prize 2014

Isamu Akasaki, Hiroshi Amano and Shuji Nakamura

E=hc/

Typical HEMTstructureto 160 GHz10 W/mm

U.K. Mishra, P. Parikh, Y.F. Wu: AlGaN/GaN HEMTs: An overview of device operation and applications


Thermal conductivitydiamond: reaching 2000 Wm-1°C-1

copper: 400SiC: 360-490graphene: 5000



OUTLINE

Microscopy: Philips CM20 and JEOL 3010 at MFA

FEI Titan Jülich

TEM sample prep.: Ar+ ion milling, Technoorg-Linda ion millerdifficulties in cuttinglong process


Nitrogen RF plasma source MBE growth

5x5 mm large single crystalline diamond pieces E6 (http://www.e6.com)

with different orientation (100, 110, 111)


GaN HEMT grown on diamondGaN HEMT grown on diamond

http://www.e6.com/

GaN grown on diamond (111)

overview of the entire layer(left after chemical etching)

numerous inversion domains close to the surface

Epitaxy:(0002)GaN//(111)diamond

and (1010)GaN//(220)diamond.


overview of the entire layer (after chemical etching)

interface regionEpitaxy:

(0002)GaN//(022)diamondand (1010)GaN//(400)diamond.


interface region

Near surface region (chemically etched!)

two different domains: [1010] and [1120] zonescommon reflection spots in the 0002 direction

(0002)GaN//(400)diamond and

(1120)GaN//(022)diamond, or (1010)GaN//(022)diamond

GaN grown on diamond (001) (111)

IDs are formed already on the surface of diamond during the AlN growth.


Nitridation supressed the formation of IDs.60 min at 150oC

FEI Titan

B. Pécz et al. Diamond & Related Materials 34 (2013) 9–12

GaN grown on diamond 110

Nitridation supressed the formation of IDs.

N-polarity is determinedby CBED

Polarity of the grown layer

GaN short vector points to the surface (N-polarity)


Recipe can give us GaN on poly-diamond as wellreasonable quality: (002): FWHM=1.92 deg

(114): FWHM=2.0 deg


AlGaN/GaN HEMT Grown by Nitride MBE on (111) Diamond

M. Alomari et al.; Electronic Lett., 46 (2010), 299

Sample preparation

• Deposition of passivating SiO2/SiN film

• Deposition of a thin amorphous Si layer (conductivity is necessary for BEN)• Growth of diamond by hot filament CVD technique (Tfilament = 2200 C)

from CH4/H2 gas mixture (0.3-0.75 %, p = 1.5-3 kPa)BEN (bias enhanced nucleation) at 700-800 C Diamond growth at 700 C substrate temperatureDuration: about 50 hours (~5 m diamond)

diamond film grown over InAlN/GaN HEMT


The lateral grain size of the polycrystalline diamond is in the order of 100 nm.

The principal phases at the interface (GaN and polycrystalline Si and diamond) are identified by electron diffraction.


High resolution TEM pictures of the nucleation zone between the Si and diamond films show plenty of cubic SiC nanoparticles embedded in an amorphous phase. The growth of the diamond film starts in this region, too.


TEM image and electron diffraction pattern of diamond grown over an InAlN/GaN HEMT structure (nucleated at 800 C)


Sample preparationGrowth conditions

High resolution electron micrograph of the of the InAlN/GaN heterostructure with the passivating amorphous SiO2 film deposited on top.


Alomari M, Dipalo M, Rossi S, Diforte-Poisson M-A, Delage S, Carlin J-F, Grandjean N, Gaquiere C, Tóth L, Pécz B, Kohn E

Diamond and Related Materials, 20, 2011, Pages 604–608

Thermal barrier resistance is high

• An alternative strategy to mitigate the surface roughening consists in coating the substrate with amorphous Si interlayer (a-Si) thin enough to be consumed during BEN (e.g. 10 nm), thus broadening the application essentially to non-Si substrates.

–reduced interfacial roughness (RMS now in the nm-range) with lower density of pits due to less-aggressive H-plasma etching CH4/H2 ratio was increased substrate T was decreased to 750oC.

–a transition zone 10 to 20 nm thick

–Minimum TBR of 3 x 10-9 m2 K W-1 (> one order of magnitude lower) with an average value of 5 x 10-9 m2 K W-1 (one order of magnitude improvement)

parameter Heat up BEN Growth Cool down

time (h:m) 00:40 02:00 variable 00:40

Pressure (kPa) 1.5 1.5 1.5 1.5

H2 (sccm) 400 400 400 400

CH4 (%) 0 1.0 0.2 to 0.6 0

T_filam (°C) from RT ↑ 2130 2130 ↓ to RT

T_sub (°C) from RT ↑ 830 825 ↓ to RT

V_grid (V) 0 45 0 0

V_bias (V) 0 -200 0 0

Optimizing Near-Interface Thermal Conductivity of NCD Thin Films

Nucleation region /3: HRTEM of the sample with a-Si interlayer

In this sample:• The transition zone has

thickness below 10 nm• SiC grains were clearly identified,

with size of 1-2 nm • The electron diffraction pattern

shows only the single crystal Si

pattern and the diamond phase.

No polycrystalline or amorphous

Si phases are visible (the regular

lattice of strong diffraction spots

all belong to the Silicon single

crystal substrate).

The interface diamond/Si[HRTEM]

Nucleation region: HRTEM of the sample with a-Si interlayer

The interface diamond/Si[HRTEM]

Interface properties are optimized.


integration of graphene sheets into nitride devices

Direct growth onto graphene failed.


smooth surface

dislocation density ~3 x 109 cm-2

A. Kovács, M. Duchamp, R.E. Dunin-Borkowski, R. Yakimova, P. L. Neumann, H. Behmenburg, B. Foltynski, C. Giesen, M. Heuken and B. Pécz: Graphoepitaxy of High-Quality GaN Layers on Graphene/6H–SiC, Advanced Materials Interfaces, 2 (2015) DOI: 10.1002/admi.201400230

AlN growth on continuous graphene

Al and Si EDXS maps superimposed onto a HAADF STEM image

HAADF STEM image, Si, C and Al EDXS maps recorded using a FEI Titan ChemiSTEM at 200 kV.


typically 3 layers of graphene, but sometimes 5 are observed


BF

DF


AlN AlN

GaN GaN

Al and Ga EDXS maps overlapped on HAADF STEM image

Al and Ga distribution extracted as a line-scan EDXS and HAADF STEM image as reference.


Images of the control sample deposited without graphene layers on 6H-SiC. (a) SEM image of the surface recorded using a secondary electron detector. (b) Cross-sectional ADF STEM image.


• lithographically patterned graphene oxide to improve heat dissipation in light-emitting diodes (LEDs). N. Han et al., Nat. Comm. 2013, 4, 1452.

• ZnO coating on O2 plasma treated graphene layers to grow high quality GaN layers K. Chung, K.C.-H. Lee and G.C. Yi, Science 2010, 330, 655.

• thermal heat-escaping channels from graphene layers on the top of AlGaN/GaN transistorsZ. Yan, G. Liu, J.M. Khan, A.A. Balandin, Nat. Comm. 2012, 3, 827.


Summary:

Device structures are grown successfully on diamond.

Single crystalline GaN can be grown on poly-diamond as well.

Diamond film with columnar microstructure can be grownby CVD - promising for heat spreading application.

Graphene layers inserted into nitride devices may help theheat dissipation


Acknowledgement:

J. Lábár (MFA), L. Tóth, Á. Barna, P. Neumann, MFA Budapest

M. Alomari, M. Dipalo, S. Rossi, E. Kohn, Ulm University

A. Georgakilas, FORTH, Heraklion, Crete

M-A. di Forte-Poisson, S. Delage, Alcatel-Thales III-V lab

H. Behmenburg, B. Foltynski, C. Giesen, M. Heuken, AIXTRON SE

A.Kovács, R. D. Borkowski, Jülich

R.Yakimova, Linköping University


Thank you for your attention!

research institute for technical physics and materials science of the hungarian academy of sciences...

Documents