Ultrafast density-and-temperature-dependent carrier dynamics in a quantum dots-in-a-well heterostructure

The incorporation of semiconductor quantum dots into different heterostructures for applications in nanoscale photodetection, lasing and amplification has been an active area of research in recent years. Here, we use ultrafast differential transmission spectroscopy to temporally and spectrally resolve density-and-temperature-dependent carrier dynamics in an InAs/InGaAs quantum dots-in-a-well (DWELL) heterostructure. In our experiments, electron-hole pairs are optically injected into the three dimensional GaAs barriers, after which we monitor carrier relaxation into the two dimensional InGaAs quantum wells and the zero dimensional InAs quantum dots by tuning the probe photon energy. We find that for low photoinjected carrier densities, carrier capture and relaxation are dominated by Auger carrier-carrier scattering at low temperatures, with thermal emission playing an increasing role with temperature. At low temperatures we also observe excitation-dependent shifts of the quantum dot energy levels. In contrast, high density measurements reveal an anomalous induced absorption at the quantum dot excited state that is correlated with quantum well population dynamics. Our experiments provide essential insight into carrier relaxation across multiple spatial dimensions and reveal unique Coulomb interaction-induced phenomena, with important implications for DWELL-based lasers and amplifiers.