1. Department of Physics, National Taiwan University, Taipei, Taiwan 10617, Republic of China
2. Department of Electronic Engineering, De Lin Institute of Technology, Tuchen City, Taipei County, Taiwan 23646, Republic of China
3. Department of Physics, National Taiwan Normal University, Taipei, Taiwan 106, Republic of China
4. Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan 202, Republic of China
5. Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China