Department of Physics, Wuhan University, Wuhan 430072;
Department of Physics, Wuhan University, Wuhan 430072;
Department of Physics, Wuhan University, Wuhan 430072;
Hebei Semiconductor Research Institute, Shijiazhuang 050051;
Hebei Semiconductor Research Institute, Shijiazhuang 050051;
Hebei Semiconductor Research Institute, Shijiazhuang 050051;