Digital-Alloy Bragg Mirrors in High-Q Microcavities for Polariton Lasing

TL;DR

This paper introduces a novel digital-alloy approach to fabricating high-Q GaAs-based microcavities with reduced interface roughness and improved optical tuning, achieving low-threshold polariton lasing with high quality factors.

Contribution

The study presents a new digital-alloy design for Bragg mirrors in microcavities, enhancing fabrication control and optical performance for polariton lasing applications.

Findings

Achieved a polariton-lasing threshold of ~570 W/cm².

Fabricated microcavities with a high Q factor of about 5.4 x 10^4.

Exceeds theoretical Q factor estimates by nearly a factor of two.

Abstract

We present an approach to the molecular-beam epitaxy of high-Q planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors (DBRs) are replaced by short-period GaAs/AlAs superlattices (digital alloys) with similar optical properties. This design enables a significant reduction of interface roughness, precise control of the quarter-wavelength optical thickness and the effective Al content, suppression of the propagation of structural defects, and efficient tuning of intrinsic absorption at the polariton emission wavelength via optimization of the superlattice parameters. Using this approach, we fabricate a microcavity with a low polariton-lasing threshold of approximately 570 W/cm$^2$ and a high experimental quality factor of about 5.4 x $10^4$. This value exceeds by almost a factor of two the theoretical estimate obtained within an equivalent ternary-alloy model. We demonstrate that accurate modeling of the stop-band characteristics and the Q factor requires incorporating the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.