1. J.S. Blakemore, J. Appl. Phys. 53, R123 (1982).
2. See, e.g. Physics and Applications of Quantum Wells and Superlattices, Eds. E.E. Mendez and K. von Klitzing (Plenum Press, New York, 1987).
3. W.T. Masselink, Y.C. Chang, H. Morkoç, D.C. Reynolds, C.W. Litton, K.K. Bajaj and P.W. Yu, Solid-State Electron. 29 205 (1986).
4. B.D. McCombe, N.C. Jarosik and J.M. Mercy, in Two-dimensional Systems: Physics and New Devices, Eds. G. Bauer, G. Kuchar and H. Heinrich (Springer-Verlag, Berlin, 1986), p.156.
5. F.M. Peeters, J.M. Shi and J.T. Devreese, in the proc. of the CAP-NSERC Workshop on: Excitations in Superlattices and Multi-Quantum Wells, (London, Ontario, Canada, 1991).