1. Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
2. Materials Department, University of California, Santa Barbara, California 93106, USA
3. Laboratoire de Physique de la Matière Condensée, Ecole polytechnique, CNRS, Université Paris Saclay, Palaiseau Cedex, France
4. Electronic and Optoelectronic System Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan