Shape-dependent optical properties of self-assembled InAs/GaAs quantum dots

Self-assembled InAs quantum dots (QDs) covered by an In0.15Ga0.85As layer with two different thicknesses were, respectively, grown on GaAs(0 0 1) substrates by a solid-source molecular beam epitaxy, and were investigated by cross-sectional transmission electron microscopy (XTEM) and photoluminescence spectroscopy under the various bias conditions. From the XTEM images the shape, especially height, of InAs QDs can be significantly modified by changing the thickness of an In0.15Ga0.85As overgrowth layer, resulting in the modification of the optical properties. With an increase in the QD height leading to more isotropic shape of QDs, the relatively better optical properties such as larger energy-level spacing between the ground states and the first excited states, and enhanced stability to the external bias conditions were demonstrated.