1. Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
2. Technology Division, Renesas Semiconductor Manufacturing Co., Ltd., Hitachinaka, Ibaraki 312-8504, Japan
3. Device Technology Division, Renesas Electronics Corporation, Hitachinaka, Ibaraki 312-8504, Japan
4. Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan