Structural and optical properties of self-assembled InAs/GaAs quantum dots covered by InxGa1−xAs (0⩽x⩽0.3)

Optical and structural investigations of InAs quantum dots (QDs) covered by ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{As}$ $\text{(0⩽x⩽0.3)}$ overgrowth layer have been systematically reported. The decrease of strain in the growth direction of InAs quantum dots covered by InGaAs layer instead of GaAs is demonstrated by transmission electron microscopy experiments. In addition, the atomic force microscopy measurement shows that the surface of InAs islands with 3-nm-thick ${\mathrm{In}}_{\mathrm{0.2}}{\mathrm{Ga}}_{\mathrm{0.8}}\mathrm{As}$ becomes flatter. However, the InGaAs islands nucleate on the top of quantum dots during the process of InAs islands covered with ${\mathrm{In}}_{\mathrm{0.3}}{\mathrm{Ga}}_{\mathrm{0.7}}\mathrm{As}.$ The significant redshift of the photoluminescence peak energy and reduction of photoluminescence linewidth of InAs quantum dots covered by InGaAs are observed. The energy gap change of InAs QDs covered by InGaAs could be explained in terms of reducing strain, suppressing compositional mixing, and increasing island height.