1. Department of Physics, University at Buffalo SUNY, Buffalo, New York 14260, United States
2. Department of Physics, St. Bonaventure University, St. Bonaventure, New York 14778, United States
3. Department of Physics, South Dakota School of Mines & Technology, Rapid City, South Dakota 57701, United States
4. Department of Computer Science, Engineering and Physics, University of Michigan−Flint, Flint, Michigan 48502, United States
5. Institute for Silicon Photovoltaics, Helmholtz-Zentrum Berlin, Berlin-Adlershof D-12489, Germany
6. Department of Electro-physics, National Chiao Tung University, Hsinchu 300, Taiwan