1. N. F. Mott, E. A. Davis: Electronic Processes in Non-Crystalline Materials (Oxford University Press, London, 1971).
2. J. Stuke, W. Brennig (Eds.): Proc. 5th Intern. Conf. Liquid and Amorphous Semiconductors, Garmisch, 1973 (Taylor and Francis, London, 1974).
3. J. M. Ziman: J. Phys. C 2, 1704 (1969).
4. R. J. Bell: Rep. Progr. Phys. 35, 1315 (1972).
5. P. Dean: Rev. Mod. Phys. 44, 127 (1972).