1. Key Laboratory of Microelectronic Devices and Integrated Technology Institute of Microelectronics of Chinese Academy of Sciences No. 3 West Road, Beitucheng Beijing 100029 China
2. University of Chinese Academy of Sciences 19 Yuquan Road, Shijingshan District Beijing 100049 China
3. SKLSM Institute of Semiconductors, Chinese Academy of Sciences P. O. Box 912 Beijing 100083 China