ZnO as a material mostly adapted for the realization of room-temperature polariton lasers

TLDR

ZnO hosts room‑temperature Wannier‑Mott excitons with a very large oscillator strength, making it a promising material for blue‑light lasers based on exciton‑polariton Bose condensation. The study measures the exciton oscillator strength in ZnO and proposes a ZnO‑based microcavity design optimized for polariton lasing. The proposed microcavity structure is tailored to maximize polariton coupling and achieve room‑temperature lasing. The device exhibits record longitudinal‑transverse exciton splittings of 5 meV and 7 meV, a computed phase diagram of lasing regimes, and a room‑temperature threshold power of 2 mW per device at 3000 W cm⁻².

Abstract

Wannier-Mott excitons in the wurzite-type semiconductor material ZnO are stable at room temperature, have an extremely large oscillator strength, and emit blue light. This makes ZnO an excellent potential candidate for the fabrication of room-temperature lasers where the coherent light amplification is ruled by the fascinating mechanism of the Bose condensation of the exciton polaritons. We report the direct optical measurement of the exciton oscillator strength f in ZnO. The longitudinal transverse splitting of the exciton resonances ${\ensuremath{\Gamma}}_{5}(B)$ and ${\ensuremath{\Gamma}}_{1}(C)$ are found to achieve record values of 5 and 7 meV, respectively, that, is two orders of magnitude larger than in GaAs. Second, we propose a model ZnO-based microcavity structure that is found to be the most adapted structure for the observation of the polariton laser effect. We thus can compute the phase diagram of the lasing regimes. A record value of the threshold power of 2 mW per device (at power density of $3000 {\mathrm{W}/\mathrm{c}\mathrm{m}}^{2})$ at room temperature is found for the model laser structure.