1. Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
2. Institute of Electronics Engineering, National Tsing Hua University, Hsinchu, Taiwan
3. Department of Photonics, National Sun Yat-sen University, Kaohsiung, Taiwan
4. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan