1. Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
2. Department of Electrophysics, National Chiayi University, Chiayi 60004, Taiwan
3. Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan
4. Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan