1. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300044, Taiwan
2. Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu 300093, Taiwan
3. National Synchrotron Radiation Research Center, Hsinchu 300092, Taiwan
4. Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300044, Taiwan
5. College of Semiconductor Research, National Tsing Hua University, Hsinchu 300044, Taiwan