Emission dynamics in QD systems: from single QD resonance fluorescence to many-emitter laser switching

Semiconductor quantum dots (QDs) have emerged in recent years as new active materials for optoelectronic devices, already used in LED’s, lasers, or optical amplifiers. A unique opportunity lies in the combination of QDs with optical microcavities, thus combining three-dimensional electronic and photonic confinement. This combination opens the possibility to exploit the Purcell effect to enhance and direct the photon emission. In this contribution, we investigate multiple facets of the emission dynamics in semiconductor QDs, ranging from the resonance fluorescence of QDs under pulsed excitation to the switch-on behavior of QD based nanolasers.
Recently the resonance fluorescence from semicoductor QDs has recieved considerable attention [1]. We show that for the case of pulsed excitation the resonance fluorescence spectrum of a quantum dot contains multiple side peaks beyond those of the Mollow triplet, due to interference effects [2]. An analytical model has been derived, which quantitatively accounts for the appearance and position of the peaks. By considering the time-dependent spectrum we demonstrate a time-ordering of the side-peaks, as shown in the left panel of Fig. 1, which is further evidence for the suggested physical explanation.
Additionally, we investigate the dynamical properties of InGaAs QD based nanolasers, combining a microscopic treatment of carrier scattering with a quantum-kinetic description of the carrier-photon interaction that also allows to study the coherence properties of the emitted light [3]. This allows for a detailed analysis of the switch-on process of nanocavity lasers showing strongly damped relaxation oscillations [4]. This behavior is driven by an ultra-fast carrier dynamics, that is shown in detail in Fig. 2. Remarkably, the timescales between the relaxation dynamics in the WL and the dynamics of the QD populations are not decoupled as it is often assumed. This is caused by the fact that the capture into the QD states is most efficient for the WL states with low quasi-momenta. Therefore, these states are constantly depleted during the first stage of the kinetics, which slows down the relaxation of the WL towards a quasi-equilibrium.