1. W. Kohn s in “Solid State Physics”, F. Seitz and D. Turnbull ed.s, (Academic, New York, 1957), v. 5, p. 257
2. E.O. Kane: in “Semiconductors and Semimetals”, R.K. Willardson and A.C. Beer ed. s, (Academic, New York, 1966) v. 1, p. 75
3. W.A. Harrison: Phys. Rev. 123, 85 (1961)
4. D.J. Ben Daniel and C.B. Duke: 152, 683 (1966)
5. This is not a universal result, but can be shown to hold for the valence and conduction band edges of direct-gap III-V compounds, see Ref. 2.