Band-edge optical properties of superlattices (SLs) can be discussed by modelling the superlattice as an effective anisotropic medium in which quasifree carriers propagate and interact. In the low barrier limit the electron and the hole motion in the confinement direction is determined by the SL potential and is replaced by an effective-mass motion with the appropriate masses obtained from the miniband dispersion. Here we present a calculational scheme which starts with the Kronig-Penney model to obtain SL miniband parameters, in particular, anisotropic effective masses for electrons and holes, and band gaps. Having these parameters, we can apply the real density matrix approach (RDMA) [1] adapted to the case of SLs [2,3], taking into account both the Coulomb interaction between the electron and the hole, and coherence between the electron-hole pairs and the radiation field. The RDMA gives the SL effective anisotropic dielectric tensor and thus enable to compute the SL optical functions. The method is applied to a ZnSe/Zn_1-xCd_xSe SL where we have computed bandoffsets, bandwidths and effective masses for the first 6 minibands (electrons, heavy- and light-holes). Then we have determined the SL dielectric tensor and computed the optical functions (absorption and reflectivity) for the case of oblique angle of incidence and for p- and s-polarisation. We also have computed ellipsometric parameters ψ, Δ and Stokes parameters. Fair agreement with available experimental data [4] has been obtained.

[1] A. Stahl and I. Balslev, Electrodynamics of the Semiconductor Band Edge, Springer Verlag, Berlin, 1987.
[2] G. Czajkowski, F. Bassani, and A. Tredicucci, Phys. Rev. B 54, 2035 (1996).
[3] G. Czajkowski, F. Bassani, and L. Silvestri, Rivista del Nuovo Cimento C 26 (5-6), pp. 1-150 (2003).
[4]. P. Guan and T. Kobayashi, Solid State Commun. 111, 311 (1999).

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