1. Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
2. Department of Physics, Center of Crystal Research, National Sun Yat-sen University, Kaohsiung, Taiwan
3. Institute of Electronics Engineering, National Tsing Hua University, Hsinchu, Taiwan
4. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan
5. Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan