1. Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, China
2. Institute of Information and Communication Technologies, Electronics and Applied Mathematics, UCLouvain, Louvain-la-Neuve B-1348, Belgium
3. Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 999077, China
4. State Key Laboratory for Chemo/Biosensing and Chemometrics, College of Semiconductors (Integrated Circuits), Hunan University, Changsha 410082, China
5. School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025, China