Effect of the growth parameters on the structure and morphology of InAs/InGaAs/GaAs DWELL quantum dot structures

The paper reports a systematic analysis by cross-sectional transmission electron microscopy of the structural parameters of molecular beam epitaxy grown multilayer InAs/InGaAs/GaAs dot-in well quantum dot (QD) lasers with a view to improve aspects such as uniformity of QD size, high spatial density, improved confinement and to reduce or eliminate defects. Based on our standard structure, previously optimised by considering only PL efficiency, we have modified parameters such as well composition and thickness and shown that the previously observed photoluminescence degradation as these parameters are increased, is due to threading dislocations. The use of the modified high-temperature growth for the barrier is shown to be effective in suppressing this dislocation mechanism. Processed laser devices with these samples exhibit room temperature threshold currents ∼30 A cm−1, amongst the best reported in the literature. Finally, the use of reduced (35 nm) barrier thickness produces both vertically correlated QDs and quantum wells, with the resulting structure resembling a 'dot within a dot' structure.