Large quantum dots with small oscillator strength

TL;DR

This study investigates the oscillator strength of large InGaAs quantum dots, revealing that exciton localization reduces the expected oscillator strength despite theoretical predictions of large values.

Contribution

It provides experimental measurements of oscillator strength and quantum efficiency in large quantum dots, highlighting the impact of alloy intermixing on exciton localization.

Findings

Measured oscillator strength is much lower than theoretical predictions.

Exciton localization occurs due to alloy intermixing.

Large quantum dots exhibit reduced oscillator strength despite Coulomb effects.

Abstract

We have measured the oscillator strength and quantum efficiency of excitons confined in large InGaAs quantum dots by recording the spontaneous emission decay rate while systematically varying the distance between the quantum dots and a semiconductor-air interface. The size of the quantum dots is measured by in-plane transmission electron microscopy and we find average in-plane diameters of 40 nm. We have calculated the oscillator strength of excitons of that size and predict a very large oscillator strength due to Coulomb effects. This is in stark contrast to the measured oscillator strength, which turns out to be much below the upper limit imposed by the strong confinement model. We attribute these findings to exciton localization in local potential minima arising from alloy intermixing inside the quantum dots.