1. Department of Microelectronic Science and Engineering School of Physical Science and Technology Ningbo University Ningbo 315211 P. R. China
2. State Key Laboratory of Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 P. R. China
3. School of Microelectronics Shandong University Ji-nan 250100 P. R. China
4. State Key Laboratory of ASIC and Systems Fudan University Shanghai 200433 P. R. China