1. Faculty of Physics and Materials Sciences Center Philipps‐Universität Marburg 35032 Marburg Germany
2. Department für Chemie Universität zu Köln Greinstraße 4‐6 50939 Köln Germany
3. Trainee at the Faculty of Physics Philipps‐Universität Marburg 35032 Marburg Germany
4. Rzhanov Institute of Semiconductor Physics Novosibirsk 630090 Russia
5. Department of Physics Novosibirsk State University Novosibirsk 630090 Russia