1. R.W. van Roosbroeck, Phys. Rev. 121, 474 (1961).
2. R.W. van Roosbroeck and H.C. Casey, Jr., Proc. 10th Int, Conf. on Physics of Semiconductors, Cambridge, M.A., Div. of Technical Infor., U.S. Atomic Energy Com., 1970.
3. R.W. van Roosbroeck and H.C. Casey, Jr., Phys. Rev. B 5, 2154 (1972).
4. M. Illegems and H.J. Queisser, Phys. Rev. B 12, 1443 (1975). For further reading, with special reference to publications in this field originating from the Pennsylvania State University:
5. J.-C. Manifacier and H.K. Henisch, Phys. Rev. B 17, 2640 (1978).