Radiative recombination in type-II ZnSe/BeTe heterostructures at high densities of free carriers

Abstract

We have studied in detail the photoluminescence in type-II ZnSe/BeTe structures with large band offsets at high optical excitation levels. Our goal is a qualitative and quantitative description of the effect of a high carrier density on the spectral and kinetic properties of the photoluminescence in such structures. We have established that a high photoexcitation density leads to a significant spectral rearrangement of the spatially indirect radiative recombination, which also depends on the thickness of the structure layers. The spectral and kinetic characteristics of the indirect optical transitions in narrow and wide structures have been found to differ qualitatively. Our numerical calculations of the effect of macroscopic electric fields on the energy spectrum of free carriers at high densities of spatially separated charges, n > 1013 cm−2, give a qualitative and quantitative description of the experimentally observed photoluminescence properties. The calculations also show that the degree of localization of the above-barrier hole states grows significantly with n under conditions of increasing band bending, which should cause a weakening of the charge separation, especially in wide structures. In an experiment, the effect manifests itself in an enhancement of the spatially direct transition at a simultaneous weakening of the indirect transition both with increasing structure width and with increasing n.