Influence of localization on the optical properties of ordered(Al0.5Ga0.5)0.52In0.48P

Using various methods of optical spectroscopy, we have investigated the influence of localization on the optical properties of ${\mathrm{CuPt}}_{B}$-type ordered $({\mathrm{Al}}_{0.5}{\mathrm{Ga}}_{0.5}{)}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}.$ Localization results from the formation of inhomogeneous domainlike microstructures during the growth of the ordered material. We compare different samples which were grown simultaneously, but on differently oriented GaAs substrates. The samples exhibit completely different microstructures which were investigated in great detail by transmission electron microscopy and x-ray measurements. Typical localization effects like inhomogeneous broadening of the photoluminescence and the Stokes shift between photoluminescence and absorption are very pronounced if the structural correlation length is comparable to the exciton Bohr radius. In this case we have found two different types of localized states, i.e., one type at higher energies close to the band edge, and one at lower energies well below the band gap. The latter is attributed to anisotropic localization centers which are not significantly influenced by ${\mathrm{CuPt}}_{B}$-type ordering. These centers produce modifications of the ordering-induced anisotropy of the photoluminescence. This phenomenon yields the possibility to obtain the mobility edge energy from the spectral dependence of the optical anisotropy. In temperature-dependent experiments, we have identified thermally activated exciton redistribution processes both within the localized states and from localized to extended states. If the excitation intensity is increased, state-filling effects produce a blue shift of the emission (moving emission). Using microphotoluminescence we demonstrate that this blueshift is not caused by a shift of single states but only by a change of their spectral weights. For high-excitation intensities above $10 {\mathrm{k}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2},$ we have identified global state filling which results in stimulated emission.