1. G.P. Agrawal, N.K. Dutta, in Semiconductors Lazers, Van Nostrand Rein-hold, New York, p. 547 (1993)
2. P.K. Nair, M. Ocampo, A. Fernandez, M.T.S. Nair, Sol. Energy Mater. 20(1990) 235. P.K. Nair, A. Fernandez, M.T.S. Nair, Proc. SPIE Int. Soc. Opt. Eng. 1149 88 (1989)
3. E. Lipovskii, V. Kolovkova, I. Petricov, A. Kang, T. Olkhovets, M. Krauss, J. Thomas, F. Silcox, Q. Wise, S.K. Shen, Appl. Phys. Lett. 71, 3406 (1997)
4. R. Dalven, in Solid State Physics, ed. by H. Ehrenreich, F. Seitz, D. Turnbull, vol. 28, Academic, New York, p. 179 (1973)
5. R.A. Cowley, Philos. Mag. 11, 673 (1965)