1. Institute of Fundamental
and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
2. Institute for Nanoscience & Engineering, University of Arkansas, W. Dickson 731, Fayetteville, Arkansas 72701, United States
3. V. Lashkaryov Institute of Semiconductor
Physics, National Academy of Sciences of Ukraine, Pr. Nauky 41, 03680 Kyiv, Ukraine