Strongly temperature-dependent recombination kinetics of a negatively charged exciton in asymmetric quantum dots at 1.55 {\mu}m

TL;DR

This study investigates how temperature influences the recombination kinetics of negatively charged excitons in asymmetric InAs quantum dots emitting at telecom wavelengths, revealing non-monotonic lifetime behavior linked to spin relaxation processes.

Contribution

It provides new insights into temperature-dependent exciton dynamics in elongated quantum dots, highlighting the role of spin relaxation and atypical confinement effects.

Findings

Charged exciton lifetime varies non-monotonically with temperature.

Relaxation involves triplet states and efficient spin-flip processes.

Atypical confinement leads to enhanced electron spin relaxation.

Abstract

We report on strongly temperature-dependent kinetics of negatively charged carrier complexes in asymmetric InAs/AlGaInAs/InP quantum dots (dashes) emitting at telecom wavelengths. The structures are highly elongated and of large volume, which results in atypical carrier confinement characteristics with $s$-$p$ shell energy splittings far below the optical phonon energy, which strongly affects the phonon-assisted relaxation. Probing the emission kinetics with time-resolved microphotoluminescence from a single dot, we observe a strongly non-monotonic temperature dependence of the charged exciton lifetime. Using a kinetic rate-equation model, we find that a relaxation side-path through the excited charged exciton triplet states may lead to such behavior. This, however, involves efficient singlet-triplet relaxation via the electron spin-flip. Thus, we interpret the results as an indirect observation of strongly enhanced electron spin relaxation without magnetic field, possibly resulting from atypical confinement characteristics.