| In this dissertation, we investigate the electronic and optical properties of self-organized InAs quantum dots grown on GaAs (001) by molecular beam epitaxy. Experimental and theoretical studies are described.; A defining feature of quantum dots is a discrete energy level structure due to localization of charge carriers. However, the luminescence spectra of large ensembles of InAs quantum dots show broad-band emission. Using cathodoluminescence spectroscopy to study small ensembles, we confirm that the electronic density of states is delta-function-like, and that the luminescence spectra of quantum dot ensembles are inhomogeneously broadened.; As a consequence of the discrete electronic structure, a carrier relaxation bottleneck in quantum dots was predicted, which could impact application of these structures to optoelectronic devices. In this dissertation, carrier relaxation in InAs dots is studied by time-resolved measurement of photoluminescence. The luminescence rise time is less than 150 ps (the measurement is limited by instrument response) and the decay time is on the order of 1 ns. The decay rate depends on transition energy and temperature in a manner consistent with thermally activated carrier transport between quantum dots. While the mechanism for rapid carrier relaxation in these structures remains unknown, our results contradict the bottleneck hypothesis.; Carrier relaxation and optical recombination in quantum dots are strongly affected by the details of the electronic level structure, which in turn depend on the dot shape. Recent work by our research group indicates that the shape of InAs/GaAs quantum dots is an elongated pyramid, with bounding facets corresponding to a family of four {lcub}136{rcub} planes. The size-dependence of the electronic structure is calculated for this shape using an eight-band effective mass approximation and including the effects of strain, determined using a valence force field model. Experimental photoluminescence polarization spectroscopy confirms key features of our electronic structure model and rules out previous models. The electron-hole exchange interaction is found to split the lowest energy exciton into four non-degenerate levels: an optically dark ground level and three optically active levels with mutually orthogonal transition dipoles oriented along the dot symmetry lines. |
