Evolution of a multimodal distribution of self-organizedInAs∕GaAsquantum dots

Abstract

Formation and evolution of a multimodal $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot (QD) ensemble during a growth interruption prior to cap layer deposition is studied. These particular kinds of QDs form self-organized after deposition of an InAs layer close to the critical thickness for elastic relaxation and after a short growth interruption. The QDs consist of pure InAs with heights varying in steps of complete InAs monolayers, have well-defined, flat, top and bottom interfaces, and show indications for steep side facets in transmission electron micrographs. QDs with a common height represent a subensemble within the QD ensemble, showing an emission peak with small inhomogeneous broadening. The evolution occurs by an increased appearance of subensembles with higher QDs and disappearance of subensembles related to smaller QDs, which accordingly dissolve. Dissolution proceeds essentially by a decrease of height, and only to a small amount by lateral shrinking. Thickness and composition of the wetting layer do not change during this process; growth and dissolution originate solely from material exchange between different QD subensembles. The evolution slows down for prolonged growth interruption, but the QD ensemble does not attain equilibrium within a time scale of minutes being eventually limited by the onset of plastic relaxation. Formation and dynamics of the observed evolution of the multimodal QD size distribution is theoretically well described by a kinetic approach, which implies strain-controlled adatom kinetics in the mass exchange between the QDs mediated by the adatom sea.