Abstract

In strained-layer superlattices (SLS's), lattice-mismatch induced strain in pseudomorphically grown structures gives rise to a preferred axis because of tetragonal distortion, making the SLS a birefringent material. As a consequence, the indices of refraction for the ordinary and the extraordinary rays are different. They vary as a function of strain. The indices of refraction may be derived from the complex dielectric constant. The imaginary part of the dielectric constant may be calculated from a knowledge of allowed energy states in the system. In the presence of strain, the energy levels change. We calculate, within a deformation potential approach, the changes in the energy levels, hence the band gap due to lattice-mismatch strain for varying compositions in the ZnSe/ZnS_xSe_1-x SLS system. We then use these results to calculate the imaginary part of the dielectric function for the system as a function of frequency. We use Kramers-Kronig to calculate the real part of the dielectric function, and from it n_o (w) and n_e(w). Using the phase matching condition for n_o(w) and n_e(w), we show the resulting strain dependence of the phase matching angle.

© 1992 Optical Society of America