1. A. Many, Y. Goldstein, N. B. Grover, Semiconductor Surfaces, Amsterdam, London, New York (1971).
2. W. Schottky, W. Deutschmann, Phys. Z. 30, 839 (1929).
3. W. Schottky, Z. Phys. 118, 539 (1972).
4. K. Heime, Solid-State Electronics 13, 1505 (1970) (with further references to the problem).
5. W. Schockly, Electrons and Holes in Semiconductors, New York (1950).