1. International College of Semiconductor Technology, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
2. Department of Electronics Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
3. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
4. Department of Electrical Engineering, National Central University, Taoyuan 320317, Taiwan
5. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA