1. Bhide V G, Ram R S, Varma S P and Om Prakash 1983Res. Ind. 28 25
2. Dance J B 1969Photoelectronic devices (London: Illiffe)
3. Despande S V 1975J. Phys. Edn 3 24
4. Gibson A F 1958Progress in semiconductors (London: Heywood & Company) Vol. 3.
5. Gutsche E and Lange H 1967Phys. Status Solidi 22 229