1. T. R. Volk, V. Yu. Salobutin, et al., Fiz. Tverd. Tela (St. Petersburg) 42(11), 2066 (2000) [Phys. Solid State 42, 2129 (2000)].
2. Y. Tomita and A. Suzuki, Appl. Phys. A: Solids Surf. 59, 579 (1994).
3. M. Li, X. Xu, et al., J. Cryst. Growth 211, 225 (2000).
4. V. V. Gladkiĭ, V. A. Kirikov, et al., Fiz. Tverd. Tela (St. Petersburg) 42(7), 1296 (2000) [Phys. Solid State 42, 1334 (2000)].
5. A. V. Knyaz’kov, N. M. Kozhevnikov, et al., Zh. Tekh. Fiz. 54(7), 1379 (1984) [Sov. Tech. Phys. 29, 801 (1984)].