1. In Situ Devices Center, School of Integrated Circuits East China Normal University Shanghai 200241 China
2. Department of Physics Shanghai Normal University Shanghai 200233 China
3. Engineering Research Center of Nanoelectronic Integration and Advanced Equipment, Ministry of Education, Department of Physics and Electronic Science East China Normal University Shanghai 200241 China
4. Institute of Optoelectronics Fudan University 2005 Songhu Road Shanghai 200438 China