1. R.L. Byer, H. Kildal, R.S. Feigelson: Appl. Phys. Lett.19, 237 (1971)
2. A. Mooradian: Rep. Prog. Phys.42, 1533 (1979)
3. W.B. Gandrud, R.L. Abrams: Appl. Phys. Lett.17, 302 (1970)
4. R.G. Harrison, F. Al-Watban, C.R. Pidgeon: Opt. Commun.5, 205 (1977)
5. S.K. Kurtz, J. Jerphagnon, M.M. Choy: InLandolt-B�rnstein, New Series, Group III, Vol. II, ed. by K.H. Hellwege and A.M. Hellwege (Springer, Berlin, Heidelberg 1979), Chap. 6, p. 671