1. State Key Laboratory of High Performance Complex Manufacturing College of Mechanical and Electrical Engineering Central South University Changsha Hunan 410083 China
2. Semiconductor Lighting Technology Research and Development Center Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China
3. Department of Photonics and Institute of Electro-Optical Engineering National Chiao-Tung University 1001 Ta Hsueh Rd. Hsinchu 300 Taiwan