1. Institute of Physics, National Academy of Sciences of Ukraine, 03680 Kyiv, Ukraine
2. Department of Applied Physics and Higher Mathematics, Kyiv National University of Technologies and Design, 01011 Kyiv, Ukraine
3. V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 03680 Kyiv, Ukraine
4. Department of Physics and Engineering Physics, Central Connecticut State University, New Britain, CT 06050, USA