1. Lindholm F. A., Ayers R. W., Proc. IEEE.56 (1968), 371.
2. Spenke E., Electronic Semiconductors, McGraw-Hill, New York 1958, p. 293 and 384.
3. Blakemore J. S., Semiconductor Statistics, Pergamon Press, London 1962, p. 87.
4. Blakemore J. S., ibid. p. 90.
5. Chakravarti A. N., Parui D. P., Czech. J. Phys.,B 23 (1973), 927.