InAs quantum dots (QDs) were grown by MBE on different InGaAs or GaAs surface layers to study the effect of the matrix on the structural and optical properties of the QDs. The d. of QDs directly grown on GaAs is 1.1 * 1010 cm-2, and increases to 2.3 * 1010 cm-2 for dots grown on a 1. nm InGaAs layer. Single-mirror light-emitting-diode (SMLED) structures with InAs QDs capped by InGaAs and grown on GaAs and InGaAs layers were fabricated to compare the electroluminescence efficiency between the 2 structures. The max. external quantum efficiency for QDs on a GaAs structure is 1.1% while that for QDs on InGaAs is 1.3%. The corresponding radiative efficiency could be deduced to be 17.5% for QDs on GaAs and 21.5% for QDs on InGaAs, resp.