1. V. Lashkaryov Institute of Semiconductors Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine
2. Physics Department, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine
3. Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
4. Center for Materials, Architectures, and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, D-09107 Chemnitz, Germany
5. Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine