1Institute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan
2Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300, Taiwan
3Department of Photonics and the Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
4Institute of Advanced Materials, Nanjing University of Technology, Nanjing 210009, China
5Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
6Department of Electrical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan