1. Rzhanov Institute of Semiconductor Physics, Novosibirsk 630090, Russia
2. Novosibirsk State University, Novosibirsk 630090, Russia
3. Institute for Physics of Microstructures RAS, GSP-105, Nizhni Novgorod 603950, Russia
4. Laboratoire Charles Coulomb, UMR CNRS 5221, University of Montpellier, Montpellier 34095, France