Ultrafast Carrier Redistribution in Single InAs Quantum Dots Mediated by Wetting-Layer Dynamics

Optical studies of single self-assembled semiconductor quantum dots (QDs) have been a topic of intensive investigation over the past two decades. Due to their solid-state nature, their electronic and optical emission properties are affected by the particular crystal structure as well as many-body-carrier interactions and dynamics. In this work, we use a master equation for microstates (MEM) model to study the carrier capture and escape from single QDs under optical nonresonant excitation and under the influence of a two-dimensional (2D) carrier reservoir (the wetting layer). This model reproduces carrier dynamics from power-dependent and time-resolved microphotoluminescence experiments . Due to the random nature of the carrier capture and escape processes, when a single QD is pumped with enough excitation power, the carrier redistribution across the available QD microstates produces an effective double-peaked excitonic decay. This double peak is characterized by a first ultrafast (subnanosecond) and a second conventional (approximately nanosecond) decay. The effective transient photoluminescence shape of the population dynamics is governed by the wetting-layer radiative decay and the exciton capture time.