Approaching transform-limited photons from nanowire quantum dots excited above-band

TL;DR

This study shows that semiconductor quantum dots embedded in specially designed nanowires can emit near-transform-limited photons even with above-band excitation, revealing new insights into exciton-phonon interactions.

Contribution

It introduces a nanowire quantum dot design that minimizes linewidth broadening under above-band excitation, achieving near-transform-limited photon emission.

Findings

Linewidths of 2x the transform limit achieved

Linewidth depends nonlinearly on power and temperature

Excess broadening not dominated by phonon dephasing at low power and temperature

Abstract

We demonstrate that, even when employing above-band excitation, photons emitted from semiconductor quantum dots can have linewidths that approach their transform-limited values. This is accomplished by using quantum dots embedded in bottom-up photonic nanowires, an approach which mitigates several potential mechanisms that can result in linewidth broadening: (i) only a single quantum dot is present in each device, (ii) dot nucleation proceeds without the formation of a wetting layer, and (iii) the sidewalls of the photonic nanowire are comprised not of etched facets, but of epitaxially grown crystal planes. Using these structures we achieve linewidths of 2x the transform limit, unprecedented for above-band excitation. We also demonstrate a highly nonlinear dependence of the linewidth on both excitation power and temperature which can be described by an independent Boson model that considers both deformation and piezoelectric exciton-phonon coupling. We find that for sufficiently low excitation powers and temperatures, the observed excess broadening is not dominated by phonon dephasing, a surprising result considering the high phonon occupation that occurs with above-band excitation.