Growth dynamics and laser applications of indium arsenide quantum dots in gallium arsenide/aluminum gallium arsenide structures

Formation and evolution of InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) in GaAs and AlAs/GaAs short period superlattice matrixes were studied in the temperature range from 350 to 500°C with emphasis on effects due to composition of adjacent surfaces. In-situ reflection high energy electron diffraction (RHEED) patterns were recorded in real time and analyzed to characterize the 2D-to-3D transition on the surface. QD formation, ripening, decay and overgrowth processes were studied in single layer and multilayer QD stacks. RHEED patterns combined with results of ex-situ atomic force microscopy were analyzed to reveal the evolution of size and shape of QDs in single-layer and stacked QD ensembles. The critical InAs coverage for QD formation was shown to be consistently higher for dots grown on AlAs overlayer than for those grown on GaAs surface. Self-assembly of multilayer QD stacks revealed the reduction of the critical thickness for dots formed in the upper layers. Direct evidence for InAs intermixing with about 6ML (monolayers) of the matrix material is found from Auger analysis during MBE overgrowth of InAs nanostructures.; Photoluminescence (PL) spectroscopy was used to study and optimize optical properties of the QDs by variation of growth parameters and introduction of a shape engineering (QD truncation) step. The shape engineering was performed by heating the structure after depositing the overlayer with a thickness close to QD height. Influence of overgrowth truncation procedure parameters and a few monolayer-thick AlAs capping layers immediately on top of self-assembled InAs QDs on the QD properties was studied.; Triple layer QD edge-emitting lasers with 1220 nm emitting wavelength exhibited a maximum saturated modal gain of 16 cm-1, characteristic temperature T0 = 380 K in the 0--50°C temperature range and maximum lasing temperature of 219°C. To further increase gain in truncated QD active medium for use in vertical cavity surface emitting lasers (VCSELs), seven layer QD structures with 20 nm of short period superlattice barriers between layers were developed. Edge-emitting lasers with 7xQDs active medium generating at 1190 nm showed maximum saturated gain of 31 cm -1.