Nanometer-scale measurements of electronic states in InAs/GaAs quantum dots

Abstract

We have investigated the origins of electronic states in individual (uncoupled) quantum dots (QDs) and the surrounding wetting layers (WLs) using a combination of cross-sectional scanning tunneling microscopy (XSTM) and scanning tunneling spectroscopy (STS). XSTM images reveal uncoupled ellipse-shaped QDs with 18 +/- 5 nm (9 +/- 3 nm) major (minor) axes. Room temperature STS spectra reveal a gradient in the effective bandgap within the QDs with smallest values near the QD core and top surfaces. The variations in effective bandgap are apparently dominated by indium composition gradients, with minimal effects due to the QD shape and strain. Indium composition gradients also dominate the effective bandgap variations in the WL.