1. Institute of Electronics; 700170 Tashkent Uzbekistan
2. Ioffe Physico-Technical Institute; 194021 St. Petersburg Russia
3. Department of Physics; Martin Luther University Halle; 06120 Halle Germany
4. Nano-Materials Lab., School of Engineering and Physical Science; Heriot-Watt University; Edinburgh EH14 4AS UK
5. Leibniz Institute for Crystal Growth; 12489 Berlin Germany
6. St. Petersburg Polytechnical State University; 195251 St. Petersburg Russia