1. D.E. Aspnes: Advances in Solid States Physics, Vol. XVII (Pergamon, Oxford 1976), p. 235
2. D.E. Aspnes: Nuovo Cimento 39, 337 (1977)
3. F. Bassani, G. Pastori Parravicini: Electronic States and Optical Transition in Solids (Pergamon, Oxford 1975)
4. M. Cardona: Solid State Physics (Suppl.) 11, 1 (1969)
5. D.L. Greenaway, K. Harbeke: Optical Properties and Band Structures of Semiconductors (Pergamon, Oxford, 1968)