1. Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan
2. Department of Electronics Engineering, Chang Gung University, Kwei-Shan, Tao Yuan 333, Taiwan
3. Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Puli 545, Taiwan
4. Department of Electrical Engineering, Yale University, 15 Prospect St, New Haven, Connecticut 06511, United States
5. Department of Chemical Engineering, Feng Chia University, Seatwen, Taichung 40724, Taiwan