1. P. Blad and J. W. Orton, Zarubezhn. Radioelecktron., No. 1, 3?50 (1981); No. 2, 3?49 (1981).
2. V. E. Dedinets, Elektron. Tekh., Ser. 2, No. 2, 83 (1984).
3. W. E. Gourthey, IEEE Trans.,MTT-25, No. 8, 697 (1977).
4. Yu. I. Tsipivka, Dep. in VINITI, Reg. No. 4167-82.
5. A. C. Sharma and S. Auluck, Phys. Status. Solidi (b),108, 587 (1981).