1. Compound Semiconductor Development Department, R&D Center, Asahi Kasei Microdevices Corporation, 2-1 Samejima, Fuji, Shizuoka 416-8501, Japan
2. Platform Laboratory for Science and Technology, Corporate R&D, Asahi Kasei Corporation, 2-1 Samejima, Fuji, Shizuoka 416-8501, Japan