1. Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique School of Electronic Science and Engineering Xi'an Jiaotong University Xi'an 710049 China
2. Department of Applied Physics School of Science Xi'an Jiaotong University Xi'an 710049 China
3. Guangdong Xi'an Jiaotong University Academy Foshan 528300 China
4. Science Program Texas A&M University at Qatar P.O. Box 23874 Doha Qatar