Composition profiling of InAs/GaAs quantum dots

We propose a simple and straightforward technique to measure the composition distribution of In(Ga)As/GaAs quantum dots (QDs). This method is based on the quantitative analysis of 002 dark field image contrast in cross-sectional transmission electron microscopy. InAs/GaAs QDs show strong InGaAs alloying resulting in the formation, prior to capping, of an inverted indium composition gradient, with higher In concentration at the top. Such a mechanism implies a large Ga mass transport from the substrate. The capping process is also investigated. It strongly affects the QD shape by dissolving the apex via surface migration of indium atoms away from the dot. (C) 2004 American Institute of Physics.