1. This idea guided Mooser and Pearson to predict semiconducting behavior in a large variety of crystalline materials. See E. Mooser and W.B. Pearson, Can. J. Phys. 34 (1956) 1369.
2. For references to their work see A.F. Ioffe and A.R. Regel, Non-Crystalline, Amorphous, and Liquid Electronic Semiconductors, in: Progress in Semiconductors, Vol. 4, Ed. A.F. Gibson (Wiley, New York, 1960) pp. 237–291.
3. For references to their work see B.T. Kolomiets, Phys. Status Solidi 7 (1964) 359,
4. For references to their work see B.T. Kolomiets, Phys. Status Solidi 7 (1964) 713.
5. For a discussion of electronic properties of amorphous materials see J. Tauc, Science 158 (1967) 1543.