Fabrication of Nanostructured GaAs/AlGaAs Waveguide for Low-Density Polariton Condensation from a Bound State in the Continuum

TL;DR

This paper demonstrates low-threshold exciton-polariton condensation in a GaAs/AlGaAs waveguide using a bound state in the continuum, enhanced by fabrication control and surface passivation techniques.

Contribution

It introduces a novel fabrication approach for long-lived polariton states using symmetry-protected bound states in the continuum in GaAs/AlGaAs waveguides.

Findings

Achieved state-of-the-art polariton condensation threshold.

Surface passivation reduces exciton quenching.

Fabrication control improves device performance.

Abstract

Exciton-polaritons are hybrid light-matter states that arise from strong coupling between an exciton resonance and a photonic cavity mode. As bosonic excitations, they can undergo a phase transition to a condensed state that can emit coherent light without a population inversion. This aspect makes them good candidates for thresholdless lasers, yet short exciton-polariton lifetime has made it difficult to achieve condensation at very low power densities. In this sense, long-lived symmetry-protected states are excellent candidates to overcome the limitations that arise from the finite mirror reflectivity of monolithic microcavities. In this work we use a photonic symmetry protected bound state in the continuum coupled to an excitonic resonance to achieve state-of-the-art polariton condensation threshold in GaAs/AlGaAs waveguide. Most important, we show the influence of fabrication control and how surface passivation via atomic layer deposition provides a way to reduce exciton quenching at the grating sidewalls.