1. Institute of Electro-Optical Engineering, National Taiwan Normal University, Taipei 11677, Taiwan
2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
3. V.E. Lashkarov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv 03028, Ukraine
4. Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10699, Taiwan