1. Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
2. Department of Photonics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
3. Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
4. Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
5. Advanced Process Research Division, AUO Corporation, Hsinchu 300, Taiwan