Optical probe of InAs/GaAs self-assembled quantum dots grown using low growth rate and growth interruptions

We have investigated the optical properties of InAs/GaAs self-assembled quantum dots (QDs), grown at 500 degrees C using a low growth rate (0.014 ML/s), growth interruptions and a two-stage capping process. The samples exhibited large-size dots with densities in the range (3-4.5) x 10(9) cm(-2). Macro-photoluminescence (macro-PL) measurements revealed the presence of five electronic sub-bands in the dots, with the ground state (GS) emission exhibiting a linewidth of similar to 70 meV. Because of the dots large size and composition dispersions, associated with the growth method, it was possible to resolve single dots emissions using micro-PL (mu-PL) excitation in the barrier layers of the as-grown samples. The sharp PL lines were detected 60-140 meV above the GS peak energy. High-resolution resonant optical excitation of the dots PL evidenced that these fine lines originate from exciton complexes confined to the GS of individual dots. Non-resonant power dependence mu-PL spectroscopy results further confirmed the occurrence of both single exciton (X) and biexciton (XX) radiative recombinations. Finally, with increasing lattice temperature up to 95 K, PL emissions from most of these nanostructures suffered the usual thermal quenching, with activation energies (E-a) ranging between 12 and 41 meV. The relatively small values of E-a suggest that the growth technique implemented here favors the formation of defects centers in the vicinity of the QDs. (c) 2007 Elsevier B. V. All rights reserved.