1. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 11529, Taiwan
2. Department of Physics, National University of Singapore, 117542 Singapore
3. SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education, Guangdong Province, Shenzhen University, Shenzhen 518060, China
4. Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
5. Department of Advanced Science and Engineering, Waseda University, Tokyo 169-8555, Japan
6. Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
7. Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan
8. Department of Applied Physics, Kagami Memorial Laboratory for Material Science and Technology, Waseda University, Tokyo 169-8555, Japan
9. School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore