Evolutional feature of InAs/GaAs quantum dots with coverages from submonolayer to a few monolayers

In this study, we demonstrate InAs/GaAs submonolayer quantum dots (SQDs) with no wetting layer (WL) formed by using the self-assembling technique. An evolutional feature was observed in the photoluminescence spectra taken from QDs whose coverages were in the range from submonolayer to a few monolayer (0.5-2.5 ML). The QD samples revealed that a small number of conventional QDs (CQDs) with a WL coexisted with the majority of SQDs with no WL. Multipeak spectra were gradually changed to single-peak profiles, and an abrupt transition from SQDs to CQDs arose before and after WL formation. A single-mode SQD ensemble was achieved by 1.5 ML, for which the coverage was close to that of the WL (1.7 ML) in which the strain field was nearly uniform over the entire layer. This showed that the sublevel of SQDs (1.32 ± 0.1 eV) was much closer to the GaAs band edge than that of CQDs (~1.2 eV).