Size dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charges on spectral diffusion

TL;DR

This study demonstrates how the height of GaAs quantum dots influences their spectral linewidths due to surface charge-induced spectral diffusion, providing insights for quantum photonic device optimization.

Contribution

It systematically investigates the size-dependent spectral broadening in GaAs quantum dots and links it to surface charge fluctuations affecting spectral diffusion.

Findings

Tall dots (~30 nm) have broad spectral lines (~5 meV)

Shallow dots (~2 nm) have resolution-limited lines (<120 μeV)

Linewidth dependence matches Stark coefficient calculations

Abstract

Making use of droplet epitaxy, we systematically controlled the height of self-assembled GaAs quantum dots by more than one order of magnitude. The photoluminescence spectra of single quantum dots revealed the strong dependence of the spectral linewidth on the dot height. Tall dots with a height of ~30 nm showed broad spectral peaks with an average width as large as ~5 meV, but shallow dots with a height of ~2 nm showed resolution-limited spectral lines (<120 micro eV). The measured height dependence of the linewidths is in good agreement with Stark coefficients calculated for the experimental shape variation. We attribute the microscopic source of fluctuating electric fields to the random motion of surface charges at the vacuum-semiconductor interface. Our results offer guidelines for creating frequency-locked photon sources, which will serve as key devices for long-distance quantum key distribution.