1. A. A. Andronov, ?Infrared and Millimetre Waves?, edited by K. J. Button, Vol. 16 (Academic Press, Orlando, 1986) p. 149.
2. I. V. Altukhov, M. S. Kagan andV. P. Sinis,Sov. Phys. ? JETP Lett. 47 (1988) 136.
3. V. I. Gavrilenko et al., Solid St. Electr. 31 (3/4) (1988) 755;R. I. Bashirov et al., Sov. Phys. ?Phys. Tech. Poluprovodn. 22 (3) (1988) 479.
4. G. L. Bir andG. E. Pikus, ?Symmetry and Deformation Effects in Semiconductors? (Nauka, Moscow, 1972).