Surface Modification of Cubic GaN Buffer Layer Grown by Metalorganic Vapor Phase Epitaxy
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SURFACE MODIFICATION OF CUBIC GaN BUFFER LAYER GROWN BY METALORGANIC VAPOR PHASE EPITAXY Akira Nagayama1,2, Ryuji Katayama1, Jun Wu1, Kentaro Onabe1, Hidetaka Sawada1, Eliko Takuma2, Hideki Ichinose2, and Yasuhiro Shiraki3, 1
Dept. of Advanced Materials Science, University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo, 113-8656, Japan, 2 Saitama Laboratory, Japan Radio Co., Ltd., 2-1-4 Fukuoka, Kamifukuoka, Saitama, 356-0011, Japan, 3 RCAST, University of Tokyo, 4-6-1 Komaba, Meguroku, 153-8904, Japan
ABSTRACT Anisotropic X-Ray diffraction (XRD) and transport properties of cubic GaN grown on GaAs substrates correspond to the features of low-temperature grown GaN (LT-GaN) buffer layer. When the LT-GaN layer is grown on the surface tilted from (001) to [1-10] with annealing in arsenic ambient, the macroscopic step edges along [1-10] direction are modified by either the ambient of thermal annealing, or substrate misorientation. A parallel conduction in GaN, GaAs, and GaN/GaAs hetero-interface was observed by photoconductivity measurements. Transmission electron microscope (TEM) observation shows that self-annihilations for (-111) B stacking faults are preferentially occurred near GaAs interface when GaN film grown on the surface tilted from (001) toward [1-10] (As step edge) is annealed in arsenic ambient. TEM observation also shows that stacking faults and dislocations are preferentially generated near GaN/GaAs interface. It is suggested that anisotropic transport properties correspond to the well-like potential generated by band bending at GaN/GaAs interface. The nearly isotropic mobility of 3,000 cm2/Vsec at 77K is obtained by improving interface property. INTRODUCTION The nitrides GaN, and their alloys appear to be promising candidates for high-power amplifiers operating at millimeter-wave region [1-3]. So far, most of the research has been focusing on the transport properties of wurtzite GaN films grown on sapphire substrates. Although sapphire is most commonly used substrate it shows huge lattice mismatch, and resulting high defect densities, which limits the lifetime of microelectronic devices. On the other hand, GaAs is one of the promising substrates to provide the possibility of monolithic integration into GaAs monolithic microwave integrated circuits (MMICs). However, an anisotropic property of GaN film grown on GaAs substrates has been observed in the X-ray diffraction reciprocal space mappings and in the Hall measurements [4-6]. In XRD reciprocal space mappings of GaN grown on vicinal GaAs substrate, the sample grown on the LT-GaN buffer layer annealed without arsine gas flowing, but with conventional hydrogen and dimethylhydrazine gas flowing, showed the enhanced generation of the hexagonal domain on the (1-11) B face, whereas the hexagonal domain on the (-111) B face was suppressed [4]. The volume ratio of hexagonal {1-101} diffraction to cubic GaN (002) was about 150. On the other hand, the sample grown on the LT-GaN buffer annealed with arsine gas flowing showed the generation of the hexagonal domains on (
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