1. Department of Physics National Sun Yat‐sen University No.70 Lien‐hai Road Kaohsiung 80424 Taiwan
2. Wuhan National Laboratory for Optoelectronics School of Optical and Electronic Information Huazhong University of Science and Technology No.1037 Luoyu Road Wuhan 430074 China
3. Department of Applied Science R.O.C. Naval Academy No.669 Junxiao Road Kaohsiung 81345 Taiwan
4. Center for Nanoscience and Nanotechnology National Sun Yat‐sen University No.70 Lien‐hai Road Kaohsiung 80424 Taiwan
5. Department of Physics The Center of Crystal Research National Sun Yat‐sen University No.70 Lien‐hai Road Kaohsiung 80424 Taiwan
6. Electrical Engineering and Computer Science University of Michigan No.1301 Beal Avenue Ann Arbor Michigan 48109‐2122 USA
7. Department of Electronics Engineering and Institute of Electronics National Chiao Tung University No.1001 University Road Hsinchu 30010 Taiwan
8. Department of Materials and Optoelectronic Science National Sun Yat‐sen University No.70 Lien‐hai Road Kaohsiung 80424 Taiwan