1. Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
2. Center for Materials, Architectures, and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, Chemnitz, Germany
3. A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentieva, 13, 630090, Novosibirsk, Russia
4. Novosibirsk State University, Pirogov, 1, 630090 Novosibirsk, Russia