| Co-Investigator(Kenkyū-buntansha) |
USUI Akira NEC Corporation, Opto-Electronic Res.Lab., Principal researcher, 光エレクトロニクス研究所, 部長
SUEMATU Takashi University of Tsukuba, Institute of Applied Physics, Lecturer, 物理工学系, 講師 (40282339)
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| Research Abstract |
A GaN substrate is desperately needed for development of practical InGaN/GaN based ultraviolet laser diodes. Purpose of this work is to obtain a free standing GaN substrate by growth of thick GaN on GaAs substrates by halide VPE.
At the beginning of the project, it was thought that cubic (zinc blende structure) GaN was practical for development of nitride based laser diodes, and growth of thick cubic GaN on GaAs(001) substrates was pursued by HVPE.Cubic phase purity of 98% for 2um thick layer and 90% for 5 um thick layer, which were the world record at that time, was obtained. An ultra violet laser diode, however, was realized in 1998on hexagonal (Wurtzite) GaN, so the subject was changed to growth of thick hexagonal GaN on GaAs (111) substrates.
The biggest problem of GaN HVPE growth on GaAs(111) was endurance of GaAs at high temperatures. It was found, however, that GaAs could stand 1000℃ growth by covering whole GaAs substrate with intermediate GaN layer grown at about 850℃. Furthermore, it was found that there was some surface flattening growth mechanism for growth of hexagonal GaN at above 1000℃.
Although a GaAs (111) substrate has polarity, GaN grown by HVPE has always Ga polarity, independently of the polarity of the substrate or the low temperature buffer layer. This is probably due to the fact that growth mechanism of HVPE is surface kinetic limited, and this is the reason why crystal quality of GaN is very high.
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