Structural and optical properties of InAs-GaAs quantum dots subjected to high temperature annealing

Annealing at higher temperature (700 degrees C) of structures with two-dimensional and three-dimensional arrays in InAs-GaAs quantum dots (QDs) results in an increase in the size and in a corresponding decrease in the indium composition of the QDs. The change in the In composition is monitored by the contrast pattern in the plan-view transmission electron microscopy (TEM) images viewed under the strong beam imaging conditions. Increase in the size of the QDs is manifested by the plan-view TEM images taken under [001] zone axis illumination as well as by the cross-section TEM images, We show that the dots maintain their geometrical shape upon annealing. Luminescence spectra demonstrate a shift of the QD luminescence peak toward higher energies with an increase in the annealing time (10-60 min) in agreement with the decrease in indium composition revealed in TEM studies. The corresponding decrease in the QD localization energy results in an effective evaporation of carriers from QDs at room temperature, and the: intensity of the QD luminescence decreases, and the intensity of the wetting layer and the GaAs matrix luminescence increase with the increase in the annealing time. (C) 1996 American Institute of Physics.