Investigations of the optical gain in a ZnO-based waveguide at low temperature
Phys. Rev. B 114, 185304 – Published 17 September, 2026
DOI: https://doi.org/10.1103/f89f-c1yw
Abstract
In this study we present a detailed spectroscopic analysis of the optical gain in a ZnO/ZnMgO waveguide microcavity benchmarked with a thick homoepitaxial ZnO layer. As a prerequisite we perform a precise determination of ZnO excitonic parameters through microreflectivity and low-excitation microphotoluminescence measurements, whose results are used as inputs for the optical gain analysis. While photoluminescence spectra and their dependence on excitation intensity reveal the presence of biexcitons in the ZnO samples, they do not participate in building up optical gain. Instead, three alternative physical processes need to be taken into account to explain optical gain in ZnO: inelastic exciton-exciton scattering; an intermediate regime involving preformed, weak-bond electron-hole Cooper pairs; and an electron-hole plasma at high carrier density. Within the current low quality factor in-plane cavity, our results are consistent with an optical gain at moderate particle densities sustained by a correlated electron-hole phase with preformed electron-hole Cooper pairs. This phase evolves to an electron-hole plasma at larger densities.
