1. Department of Physics, National Sun Yat-sen University, Kaohsiung City, Taiwan
2. Institute of Electronics Engineering, National Tsing Hua University, Hsinchu, Taiwan
3. Department of Physics, Center of Crystal Research, College of Semiconductor and Advanced Technology Research, National Sun Yat-sen University, Kaohsiung City, Taiwan
4. Department of Photonics, National Sun Yat-sen University, Kaohsiung City, Taiwan
5. Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung City, Taiwan