1. Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520, United States
2. Department
of Electro-Optical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, Taiwan 300, Republic of China
3. R&D Division, Epistar Co., Ltd., Science-based Industrial Park, Hsinchu, Taiwan 300, Republic of China