1. R. de Laer Kronig, W.J. Penney, Proc. Roy. Soc. London, 130, 499 (1930)
2. A. Nussbaum, Semiconductor Device Physics,(Prentice-Hall, Englewood Cliffs, N.J. 1962 ) Sects. 1.9 and 1. 13
3. R.A. Smith, Wave Mechanics of Crystalline Solids, 2nd edn. (Chapman and Hall, London 1969 ) Sect. 6.2
4. J.P. McKelvey, Solid-State and Semiconductor Physics, (Harper and Row, New York 1966 ) Sect. 8. 6
5. E.O. Kane, J. Phys. Chem. Solids 1, 249 (1957)