1. State Key Laboratory for Superlattices and Microstructures
2. Institute of Semiconductors
3. Chinese Academy of Sciences
4. Beijing 100083
5. China
6. State Key Laboratory of Infrared Physics
7. Shanghai Institute of Technical Physics
8. Shanghai
9. P. R. China
10. School of Physical Science and Technology
11. Southwest Jiaotong University
12. Chengdu