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. Pécz Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences MTA TTK MFA, 1121 Budapest, Konkoly-Thege M. u , Hungary

Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences High power devicesoptoelectronics blue LED---> Nobel prize 2014 Isamu Akasaki, Hiroshi Amano and Shuji Nakamura E=hc/

Typical HEMT structure to 160 GHz 10 W/mm U.K. Mishra, P. Parikh, Y.F. Wu: AlGaN/GaN HEMTs: An overview of device operation and applications Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences

Thermal conductivity diamond: reaching 2000 Wm -1 °C -1 copper: 400 SiC: graphene:5000 Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences

GaN HEMT grown on diamond CVD diamond coating for high power devices integration of graphene sheets into nitride devices OUTLINE

Microscopy: Philips CM20 and JEOL 3010 at MFA FEI Titan Jülich TEM sample prep.: Ar + ion milling, Technoorg-Linda ion miller difficulties in cutting long process Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences

Nitrogen RF plasma source MBE growth 5x5 mm large single crystalline diamond pieces E6 ( with different orientation (100, 110, 111) Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences GaN HEMT grown on diamond

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.

GaN grown on diamond (110) overview of the entire layer (after chemical etching) interface region Epitaxy: (0002)GaN//(022)diamond and(1010)GaN//(400)diamond.

GaN grown on diamond (001) interface region Near surface region ( chemically etched !) two different domains: [1010] and [1120] zones common 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.

GaN grown on diamond (111) Nitridation supressed the formation of IDs. 60 min at 150 o C 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 determined by CBED

Polarity of the grown layer  Ga  N short vector points to the surface (N-polarity)

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences Recipe can give us GaN on poly-diamond as well reasonable quality: (002): FWHM=1.92 deg (114): FWHM=2.0 deg

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences AlGaN/GaN HEMT Grown by Nitride MBE on (111) Diamond M. Alomari et al.; Electronic Lett., 46 (2010), 299

Sample preparation Deposition of passivating SiO 2 /SiN film Deposition of a thin amorphous Si layer (conductivity is necessary for BEN) Growth of diamond by hot filament CVD technique (T filament = 2200 C) from CH 4 /H 2 gas mixture ( %, p = kPa) BEN (bias enhanced nucleation) at  C Diamond growth at 700 C substrate temperature Duration: 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.

diamond film grown over InAlN/GaN HEMT 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.

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

diamond film grown over InAlN/GaN HEMT Sample preparation Growth conditions High resolution electron micrograph of the of the InAlN/GaN heterostructure with the passivating amorphous SiO 2 film deposited on top.

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences 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 CH 4 /H 2 ratio was increased substrate T was decreased to 750 o C. –a transition zone 10 to 20 nm thick –Minimum TBR of 3 x m 2 K W -1 (> one order of magnitude lower) with an average value of 5 x m 2 K W -1 (one order of magnitude improvement) parameterHeat upBENGrowthCool down time (h:m)00:4002:00variable00:40 Pressure (kPa)1.5 H2 (sccm)400 CH4 (%) to 0.60 T_filam (°C)from RT ↑2130 ↓ to RT T_sub (°C) from RT ↑830825↓ to RT V_grid (V)04500 V_bias (V) 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.

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences integration of graphene sheets into nitride devices Direct growth onto graphene failed.

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences smooth surface dislocation density ~3 x 10 9 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: /admi

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.

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences typically 3 layers of graphene, but sometimes 5 are observed

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

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

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

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences lithographically patterned graphene oxide to improve heat dissipation in light-emitting diodes (LEDs). N. Han et al., Nat. Comm. 2013, 4, ZnO coating on O 2 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 transistors Z. Yan, G. Liu, J.M. Khan, A.A. Balandin, Nat. Comm. 2012, 3, 827.

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences 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 grown by CVD - promising for heat spreading application. Graphene layers inserted into nitride devices may help the heat dissipation

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

Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sciences Thank you for your attention!