Evolution of the optical properties of InAs/GaAs quantum dots for increasing InAs coverages

The photoluminescence (PL) of InAs/GaAs heterostructures is investigated for InAs coverages, L, ranging from 0.6 to 3 monolayers (ML). For thin coverages (L less than or equal to 1.6 ML), we observe the recombination of heavy-hole excitons in InAs quantum dots (QDs) and in a 2D-InAs layer. The two PL bands shift toward low energy for increasing L. For L greater than or equal to 1.6 ML, the QD band shifts faster, while the exciton recombination in the 2D-layer vanishes. These results, confirmed by PL excitation and photoreflectivity, indicate that: a) QDs are interconnected by a two-dimensional InAs layer which allows an efficient carrier capture into the dots. b) the dot size increases with L, faster for L greater than or equal to 1.6 ML, at the expense of the 2D-layer. The peculiar temperature dependence of lineshape and peak energy of the QD band is explained in terms of exciton thermal escape and relaxation mechanisms.