Fig. 1

Growth and characterization of the quantum dots. a–f Schematic process of the quantum dot (QD) growth. a InAs is deposited on a GaAs-surface. b After deposition of ~1.5 monolayers of InAs, strain-driven QD-formation takes place. The QDs are capped with a monolayer of AlAs (c) and 2 nm GaAs (d). During these steps segregation of In atoms takes place (blue arrows) resulting in a wetting layer (WL) which is an alloy of GaAs, InAs, and AlAs. e The top part of the capped QD evaporates at 630 °C (flushing step). f The flushed QDs are overgrown with GaAs. g Scanning transmission electron microscopy image of a flushed QD. InAs appears bright, AlAs dark. h Chemical composition of the WL measured by spatially resolved energy dispersive X-ray (EDX) spectroscopy at a location without a QD (different location to g but nominally the same). i Ensemble photoluminescence (PL) at room temperature from a sample with unflushed, standard InGaAs QDs (red curve) and unflushed, AlAs-capped InGaAs QDs (black curve). The WL PL (highlighted by the red band) dominates the spectrum. The QD PL appears in the regime 1000–1300 nm. The QD-shells are labeled. j Ensemble-PL at 77 K from a sample with flushed, standard InGaAs QDs (red curve) and flushed, AlAs-capped InGaAs QDs (black curve). The flushing blue-shifts the QD-ensemble to ~900–980 nm