Carrier relaxation mechanisms and Fermi versus non-Fermi carrier distribution in quantum dot arrays formed by activated alloy phase separation

An experimental study of carrier relaxation mechanisms and carrier distribu tion in InAs-InGaAs-GaAs quantum dot (QD) arrays is presented. The structur es were investigated by resonant photoluminescence (PL) at different temper atures. For a sample with low confinement energy for electrons and holes in a QD the carrier distribution within the QD array changes from non-Fermi ( random) to Fermi (equilibrium) when temperature increases from 20 to 300 K. In contrast, for the sample with high QD confinement energy the carrier di stribution remains random even at room temperature. Near-resonant PL at 20 K reveals a series of broad phonon replicas ascribed to multiphonon relaxat ion processes involving LO phonons in the QD, in the wetting layer, at the interface and in GaAs as well as acoustic phonons. The complex distribution of InGaAs in QDs formed by activated alloy phase separation is believed to cause a dispersion of QD phonon energies and to lead to a further broadeni ng of phonon lines.