1. Department
of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
2. Department
of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
3. Institute
of Materials Research and Engineering, Agency for Science, Technology, and Research (A*STAR), Innovis, Singapore 138634
4. Institute
of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 611731, P. R. China
5. Department
of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
6. School of
Material Science and Engineering, State Key Laboratory of Advanced
Processing and Recycling of Non-Ferrous Metals in Gansu Province, Lanzhou University of Technology, Lanzhou 730050, Gansu, P. R. China