1. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan
2. Department of Physics and the Center of Crystal Research, National Sun Yat-sen University, Kaohsiung, Taiwan
3. Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
4. Department of Physics, R.O.C. Military Academy, Kaohsiung, Taiwan