Photo-draining and slow capture of carriers in quantum dots probed by resonant excitation spectroscopy

TL;DR

This study combines experimental and theoretical approaches to understand how residual charges and slow carrier capture processes affect the resonant emission of InAs/GaAs quantum dots, revealing ultra-slow relaxation dynamics.

Contribution

It introduces a detailed population model that explains carrier draining and optical gating effects, highlighting ultra-slow capture processes in quantum dots.

Findings

Carrier draining occurs on microsecond timescales.

Optical gating effectively controls quantum dot emission.

Slow Auger- and phonon-assisted processes dominate carrier dynamics.

Abstract

We investigate experimentally and theoretically the resonant emission of single InAs/GaAs quantum dots in a planar microcavity. Due to the presence of at least one residual charge in the quantum dots, the resonant excitation of the neutral exciton is blocked. The influence of the residual doping on the initial quantum dots charge state is analyzed, and the resonant emission quenching is interpreted as a Coulomb blockade effect. The use of an additional non-resonant laser in a specific low power regime leads to the carrier draining in quantum dots and allows an efficient optical gating of the exciton resonant emission. A detailed population evolution model, developed to describe the carrier draining and the optical gate effect, perfectly fits the experimental results in the steady state and dynamical regimes of the optical gate with a single set of parameters. We deduce that ultra-slow Auger- and phonon-assisted capture processes govern the carrier draining in quantum dots with relaxation times in the 1 - 100 microsecond range. We conclude that the optical gate acts as a very sensitive probe of the quantum dots population relaxation in an unprecedented slow-capture regime.