1. A.V. Rzhanov Institute of Semiconductor Physics, pr. Lavrentjeva,
13, 630090 Novosibirsk, Russia
2. Novosibirsk State University, Pirogov str. 2, 630090 Novosibirsk, Russia
3. Semiconductor Physics, Technische Universität Chemnitz, D-09107 Chemnitz, Germany