[1] Natl Acad Sci Belarus, Joint Inst Solid State & Semicond Phys, Minsk 220072, BELARUS
[2] Helmholtz Zentrum Berlin Mat & Energie GmbH, D-14109 Berlin, Germany
[3] Inst Elect Mat Technol, PL-01919 Warsaw, Poland
[4] Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland