1. Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2. Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan, Taiwan
3. Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan
4. Device Department, United Microelectronics Corporation, Tainan Science Park, Tainan, Taiwan