Localization of excitons in thermally annealed ${\mathrm{In}}_{0.14}{\mathrm{Ga}}_{0.86}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum wells studied by time-integrated four-wave mixing

We have studied the effects of thermal annealing on the localization of excitons in ${\mathrm{In}}_{0.14}{\mathrm{Ga}}_{0.86}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ multiple quantum wells by means of linear spectroscopy and time-integrated four-wave mixing. The localization occurs due to interface roughness resulting from well width fluctuations, respectively, alloy fluctuations on a length scale comparable to the exciton Bohr radius. Due to lateral inhomogeneities of the diffusion of In out of the quantum well and of Ga into the quantum well during the annealing, we observe a structural transition of the localization potential for annealing temperatures greater than 850 °C. This transition is characterized by the development of disorder on a length scale larger than the exciton Bohr radius.