Size distribution in self-assembled InAs quantum dots on GaAs (001) for intermediate InAs coverage

Abstract

Photoluminescence spectroscopy is used to investigate the size distribution of InAs quantum dots embedded in GaAs quantum wells as function of substrate temperature and InAs coverage. For intermediate InAs coverage, quantum dots of more than one distinct size class coexist with each other. We show that the quantum dot size distribution is bimodal for relatively high growth temperatures ${(T}_{G}\ensuremath{\cong}505\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ and becomes multimodal for relatively low growth temperatures ${(T}_{\mathrm{G}}\ensuremath{\cong}420\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ with growth interruptions. We explain this behavior in terms of two distinct thresholds for dot formation: (i) the minimum InAs coverage which can lead to islanding and (ii) the coverage consistent with the optimal dot size for the given growth conditions. Further, thermally activated electron transfer from dots in the smaller size class to those in the larger size class is investigated using the temperature dependence of the photoluminescence.