1. S. H. Hagen and A. W. C. Kemenade, Phys. Status Solidi A 33, 97 (1976).
2. Yu. A. Vodakov, N. Zhumaev, B. P. Zverev, et al., Fiz. Tekh. Poluprovodn. (Leningrad) 11, 373 (1977) [Sov. Phys. Semicond. 11, 214 (1977)].
3. É. E. Violin and G. F. Kholuyanov, Fiz. Tverd. Tela (Leningrad) 6, 1696 (1964) [Sov. Phys. Solid State 6, 1331 (1964)].
4. H. Kuwabara and S. Yamada, Phys. Status Solidi A 30, 739 (1975).
5. A. I. Veinger, Yu. A. Vodakov, Yu. I. Kozlov, et al., Pis’ma Zh. Tekh. Fiz. 6, 1319 (1980) [Sov. Tech. Phys. Lett. 6, 566 (1980)].