[1
]Institute of Technical Physics, Faculty of Materials Science and Applied Chemistry,
Riga Technical University, 3/7 Paula Valdena Str., LV-1048 Riga, Latvia
[2
]Institute of Applied Research, Vilnius University, Sauletekio Ave. 3, Vilnius 10222,
Lithuania
[3
]Department of Semiconductor Physics, Vilnius University, Sauletekio Ave. 3, Vilnius
10222, Lithuania
[4
]Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., 1063 Riga,
Latvia
[5
]Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu
432-8011, Japan