1. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Department of Physics, National Taiwan University, Taipei 10617, Taiwan
3. Compound Semiconductor Solar Cell Department, Next Generation Solar Cell Division, Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
4. School of Electronics and Computer Science, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom
5. Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan