A carrier relaxation bottleneck probed in single InGaAs quantum dots using integrated superconducting single photon detectors

TL;DR

This study investigates the carrier relaxation bottleneck in single InGaAs quantum dots using integrated superconducting single photon detectors, revealing how increased carrier injection speeds up relaxation and how charge carriers in surrounding layers help bypass the bottleneck.

Contribution

It provides new insights into the relaxation dynamics and bottleneck mechanisms in quantum dots, highlighting the role of charge carriers in the wetting layer in circumventing relaxation limits.

Findings

Relaxation time decreases from 1.22 ns to 0.10 ns with increased carrier injection.

Relaxation bottleneck is identified at low excitation levels.

Auger-type scattering helps bypass phonon relaxation bottleneck.

Abstract

Using integrated superconducting single photon detectors we probe ultra-slow exciton capture and relaxation dynamics in single self-assembled InGaAs quantum dots embedded in a GaAs ridge waveguide. Time-resolved luminescence measurements performed with on- and off-chip detection reveal a continuous decrease in the carrier relaxation time from 1.22 $\pm$ 0.07 ns to 0.10 $\pm$ 0.07 ns upon increasing the number of non-resonantly injected carriers. By comparing off-chip time-resolved spectroscopy with spectrally integrated on-chip measurements we identify the observed dynamics in the rise time ($\tau_r$) as arising from a relaxation bottleneck at low excitation levels. From the comparison with the temporal dynamics of the single exciton transition with the on-chip emission signal, we conclude that the relaxation bottleneck is circumvented by the presence of charge carriers occupying states in the bulk material and the two-dimensional wetting layer continuum. A characteristic -2/3 power law dependence of the rise time is observed suggesting Auger-type scattering between carriers trapped in the quantum dot and the two-dimensional wetting layer continuum which circumvents the phonon relaxation bottleneck.