1. Department of PhysicsNational Sun Yat‐Sen University Kaohsiung 804 Taiwan
2. Department of Applied ScienceR.O.C. Naval Academy Kaohsiung 813 Taiwan
3. Center for Nanoscience and NanotechnologyNational Sun Yat‐Sen University Kaohsiung 804 Taiwan
4. Center of Crystal ResearchNational Sun Yat‐Sen University Kaohsiung 804 Taiwan
5. Department of Materials and Optoelectronic ScienceNational Sun Yat‐Sen University Kaohsiung 804 Taiwan
6. Institute of Electronics EngineeringNational Tsing Hua University Hsinchu 30013 Taiwan
7. Department of Electronics Engineering and Institute of ElectronicsNational Chiao Tung University Hsinchu 30010 Taiwan R. O. C.