1. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan
2. Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
3. Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
4. Institute of Electronics Engineering, National Tsing Hua University, Hsinchu, Taiwan
5. Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan
6. Department of Physics, Republic of China Military Academy, Kaohsiung, Taiwan