1. L. V. Keldysh,JETP 47 (1964) 1945.
2. B. M. Ashkinadze, A. I. Bobrysheva, E. V. Vitiu, V. A. Kovarsky, A. V. Lelyakov, S. A. Moscalenko, S. L. Pyshkin, andS. I. Radautsan,Proc. Int. Conf. Phys. Semicond. (Moscow 1968)1 189?193.
3. V. A. Kovarsky,JETP 57 (1969) 12?17.
4. Idem, ibid 57 (1969) 1613?1622.
5. N. A. Goryunova, S. L. Pyshkin, A. S. Borschevsky, S. I. Radautsan, G. A. Kalyushnaya, Yu. T. Maksimov, andO. G. Peskov,Proc. Int. Symp. Cryst. Growth of IUC Congr. (Moscow 1966), Rost Kristallov,VIII part II (1968) 84?89.