1. Department of Physics and Microelectronics Engineering, Kyrgyz-Russian Slavic University, Bishkek, Kievskaya Str. 44, 720000, Kyrgyz Republic
2. Freie Universität Berlin, Fachbereich Physik, Arnimalleee 14, 14195 Berlin, Germany
3. Physics Department, CSU Fresno, 2345 East San Ramon Ave., M/S 37 Fresno CA 93740-8031, USA