[1] Ioffe Inst, St Petersburg 194021, Russia
[2] Peter Great St Petersburg Polytech Univ, St Petersburg 195251, Russia
[3] Rzhanov Inst Semicond Phys, Novosibirsk 630090, Russia
[4] Lobachevski State Univ, Nizhnii Novgorod 603950, Russia
[5] Zhejiang Univ, State Key Lab Silicon Mat, Hangzhou 310027, Zhejiang, Peoples R China
[6] Zhejiang Univ, Dept Mat Sci & Engn, Hangzhou 310027, Zhejiang, Peoples R China