1. Semiconductor Physics, Institute of Physics, Chemnitz University of Technology 1 , Chemnitz, Germany
2. Center for Materials, Architectures, and Integration of Nanomembranes (MAIN), Chemnitz University of Technology 2 , Chemnitz, Germany
3. A.V. Rzhanov Institute of Semiconductor Physics 3 , Novosibirsk, Russia
4. Novosibirsk State University 4 , Novosibirsk, Russia