Influence of In/Ga intermixing on the optical properties of InGaAs/GaAs quantum dots

We report on the impact of thermal annealing of buried InGaAs quantum dots (QDs) on the eigenstate energies and their inhomogeneous broadening due to size fluctuations. Application of annealing temperatures (T-A) of up to 700 degrees C for 30 min results in a blue shift of the QD ground state luminescence of 150 meV accompanied by a strong reduction of sublevel separation and inhomogeneous broadening. At the same time the wetting layer luminescence is only slightly shifted, resulting in a strongly decreased localization energy of the QDs. With increasing annealing temperature the photoluminescence peak broadening due to the QDs size distribution shows a distinct maximum and subsequently decreases below the value of as grown QDs. These observations qualitatively agree with calculations for a simple model system of spherical QDs assuming Fickian interdiffusion of dot and barrier material. Our results demonstrate that the growth temperatures (T-Gr) applied after deposition of the QDs strongly affect their properties. Thus for fabrication of QD based devices in the InGaAs/GaAs system a compromise for the choice of TGr has to be made in order to achieve both high carrier localization energies in the QDs (low T-Gr) and high material quality of the cap layers (high T-Gr). (C) 1998 Elsevier Science B.V. All rights reserved.