1. Department
for Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
2. School
of Semiconductor and Chemical Engineering, Semiconductor Physics Research
Center, Chonbuk National University, Jeonju 561-756, Republic of Korea
3. Department
of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 790-784, Republic of Korea