1. Institute of Electronics Engineering, National Tsing Hua University, Hsinchu, Taiwan
2. Department of Physics, Republic of China Military Academy, Kaohsiung, Taiwan
3. Department of Physics, Center of Crystal Research, College of Semiconductor and Advanced Technology Research, National Sun Yat-sen University, Kaohsiung, Taiwan
4. Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
5. Department of Photonics, National Sun Yat-sen University, Kaohsiung, Taiwan
6. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan
7. Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan
8. Department of Computer Science, Boston University, Boston, MA, USA