Effect of the lower and upper interfaces on the quality of InAs/GaAs quantum dots

The aim of this work is to influence quantum dot (QD) formation by improving the lower and upper InAs/GaAs QD interface quality. QD properties were studied by reflectance anisotropy spectroscopy, atomic force microscopy and high resolution transmission electron microscopy. All structures were prepared by low pressure metal organic vapor phase epitaxy. Concerning the lower interface, a good epitaxial surface planarity is required for QD formation with high QD density and narrow size distribution. Therefore the growth conditions of the QD buffer layer are very important. We demonstrate the improvement of the QD size distribution and homogeneity, when the growth rate of the buffer layer was decreased. The upper QD interface is formed during the covering process. InAs quantum dots were capped by GaAs or by GaAsSb. The presence of Sb atoms in covering layer strongly influences the interface abruptness. In the case of GaAs covering layer, an InGaAs layer with gradual decrease of In concentration is unintentionally formed at the interface between InAs and GaAs. The presence of Sb in GaAsSb covering layer helps to form abrupt interface between InAs and covering layer. However, enhanced surfacting of In atoms was observed for GaAsSb SRL. An optimal GaAsSb composition profile is suggested to prevent dissolution of QDs during the covering process and to minimize the amount of surfacting In atoms. (C) 2014 Elsevier B.V. All rights reserved.