Influence of localization on the optical properties of ordered (A(0.5)Gao(0.5))(0.52)In0.48P

Using various methods of optical spectroscopy, we have investigated the inf luence of localization on the optical properties of CuPtB-type ordered (Al0 .5Ga0.5)(0.52)In0.48P Localization results from the formation of inhomogene ous domainlike microstructures during the growth of the ordered material. W e compare different samples which were grown simultaneously, but on differe ntly oriented GaAs substrates. The samples exhibit completely different mic rostructures which were investigated in great detail by transmission electr on microscopy and x-ray measurements. Typical localization effects like inh omogeneous broadening of the photoluminescence and the Stokes shift between photoluminescence and absorption are very pronounced if the structural cor relation length is comparable to the exciton Bohr radius. In this case we h ave 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 whic h are not significantly influenced by CuPtB-type ordering. These centers pr oduce modifications of the ordering-induced anisotropy of the photoluminesc ence, This phenomenon yields the possibility to obtain the mobility edge en ergy from the spectral dependence of the optical anisotropy. In temperature -dependent experiments, we have identified thermally activated exciton redi stribution processes both within the localized stares and from localized to extended stares. If the excitation intensity is increased, state-filling e ffects produce a blue shift of the emission (moving emission). Using microp hotoluminescence we demonstrate that this blueshift is not caused by a shif t of single states but only by a change of their spectral weights. For high -excitation intensities above 10 kW/cm(2), we have identified global state filling which results in stimulated emission.