Structural and optical properties of self-assembled InAs/GaAs quantum dotscovered by InxGa1-xAs (0 <= x <= 0.3)

Optical and structural investigations of InAs quantum dots (QDs) covered by InxGa1-xAs (0 less than or equal to x less than or equal to 0.3) overgrowt h layer have been systematically reported. The decrease of strain in the gr owth direction of InAs quantum dots covered by InGaAs layer instead of GaAs is demonstrated by transmission electron microscopy experiments. In additi on, the atomic force microscopy measurement shows that the surface of InAs islands with 3-nm-thick In0.2Ga0.8As becomes flatter. However, the InGaAs i slands nucleate on the top of quantum dots during the process of InAs islan ds covered with In0.3Ga0.7As. The significant redshift of the photoluminesc ence peak energy and reduction of photoluminescence linewidth of InAs quant um dots covered by InGaAs are observed. The energy gap change of InAs QDs c overed by InGaAs could be explained in terms of reducing strain, suppressin g compositional mixing, and increasing island height. (C) 2000 American Ins titute of Physics. [S0021-8979(00)04018-4].