1. Center for Opto-Electronic Materials and Devices; Post-Silicon Semiconductor Institute; Korea Institute of Science and Technology (KIST); Seoul 02792 Republic of Korea
2. Microsystems Technology Laboratories; Massachusetts Institute of Technology (MIT); Cambridge MA 02139 USA
3. Institute of Physics and Applied Physics; Yonsei University; Seoul 03722 Republic of Korea
4. School of Electrical Engineering; Korea University; Seoul 02841 Republic of Korea
5. Division of Nano & Information; KIST School; Korea University of Science and Technology; Seoul 02792 Republic of Korea