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