1. School of Semiconductor and Chemical Engineering, and Semiconductor Physics Research CenterChonbuk National UniversityJeonju561‐756Republic of Korea
2. Department of Mechanical Engineering and Texas Center for Superconductivity at the University of Houston (TcSUH)University of HoustonHoustonTexas77204‐4006USA
3. Center for Compound Semiconductors and School of Electrical and Computer EngineeringGeorgia Institute of TechnologyAtlantaGeorgia30332‐0250USA