1. Useful general references are the proceedings of biennial conferences on Amorphous and Liquid Semiconductors, the most recent of which have been (1) Ann Arbor (1971), J. Non-Cryst. Solids 8–10 (1972); (2) Garmisch (1973), published as Amorhous and Liquid Semiconductors (Taylor and Francis 1970: (3) Leningrad (1975), published as Structure and Properties of Non-Crystalline Semiconductors (Nauka, Leningrad 1976); (4) Edinburgh (1977), published as Proceedings of the 7th International Conference on Amorphous and Liquid Semiconductors. Also, Amorphous and Liquid Semiconductors, editor J. Tauc, published by Plenum Press, New York (1974).
2. Physics of Structurally Disordered Solids, editor S.S.Mitra, published by Plenum Press, New York (1976).
3. Tetrahedrally Bonded Amorphous Semiconductors, edited by Brodsky, Kirkpatrick and Weaire, American Institute of Physics, Vol. 20 (1974).
4. Structure and Excitations of Amorphous Solids, edited by Lucovsky and Galeener, American Institute of Physics, Vol.31 (1976).
5. Several sources give classifications into groups. See, for example, H. Fritzsche in Amorphous and Liquid Semiconductors, editor J.Tauc, reference 1.