Intraband carrier relaxation in quantum dots embedded in doped heterostructures

The effect of bulk plasmon-LO-phonon excitations inherent to doped areas of semiconductor heterostructures upon the electronic dynamics of quantum dots spaced apart from the areas is studied. An effective mechanism of intraband carrier relaxation in quantum dots is proposed for such heterostructures. The mechanism involves interaction between the quantum dot carriers and the electric potential induced by bulk plasmon-LO-phonon modes of the doped areas. It is shown that the interaction opens two relaxation windows with the spectral positions and widths controlled, correspondingly, by the free-carrier concentrations and the bulk plasmon-LO-phonon mode dispersion of the doped areas. The relaxation rates related to the mechanism are calculated for quantum dots spaced apart by different distances z0 from doped substrate (the area) with the different free-carrier concentrations n0. The estimations carried out for InAs quantum dots and the GaAs substrate yield the relaxation rates of about 108 s-1 for n0=1018 cm-3 and z0=100 nm. The rates increase by two to three orders of magnitude with decreasing the distance down to 20 nm. A manifestation of the mechanism is shown for a system of self-assembled InAs/GaAs quantum dots separated by a distance of 100 nm from an n-doped GaAs substrate by means of the photoluminescence spectroscopy. From the experiment it has been found that L- and L+ plasmon-LO-phonon modes of the GaAs substrate are involved in the intraband carrier relaxation in the quantum dots. The data are in good agreement with the theoretical predictions