1. Faculty of Materials Science and Applied ChemistryInstitute of Technical Physics, Riga Technical UniversityP. Valdena 3/7Riga LV‐1048Latvia
2. Faculty of Materials Science and Applied Chemistry, Institute of Silicate MaterialsRiga Technical UniversityP. Valdena 3/7Riga LV‐1048Latvia
3. Research Institute of Electronics of Shizuoka University3‐5‐1, JohokuNaka‐ku Hamamatsu 432‐8011Japan
4. V.E Lashkaryov Institute of Semiconductor Physics NAS of UkraineProspect Nauky 45KievUkraine