1. Fujian Provincial Key Laboratory of Semiconductors and Applications, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen University, Xiamen 361005, P.R. China
2. Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
3. Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
4. Xiamen University Malaysia, 439000 Sepang, Selangor, Malaysia