Xiaoxiang Wu1, Haiguang Ma1, Han Yin1, Danfeng Pan1, Junzhuan Wang1, Linwei Yu1,*, Jun Xu1, Yi Shi1, Kunji Chen1
1 National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, 210093 Nanjing, P. R. China
