Excitonic Mechanisms of Stimulated Emission in Low-Threshold ZnO Microrod Lasers with Whispering Gallery Modes

• Published in: Materials Vol. 15; no. 24; p. 8723
• Main Authors: Tarasov, Andrey P, Muslimov, Arsen E, Kanevsky, Vladimir M
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.12.2022; MDPI
• Subjects: Emission analysis; excitonic lasing; Excitons; Holes (electron deficiencies); Inelastic scattering; Lasers; Lasing; low-threshold lasing; Microcrystals; Microlasers; microrod; Microscopy; optical gain; Photoexcitation; Q factors; Radiation; Red shift; Room temperature; Stimulated emission; Whispering gallery modes; Zinc oxide; Zinc oxides; ZnO; Russia; exciton-exciton scattering; exciton-electron scattering; excitonic lasing; low-threshold lasing; two-phonon assisted exciton recombination; ZnO; optical gain; microrod; whispering gallery modes; stimulated emission
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15248723

Whispering gallery mode (WGM) ZnO microlasers gain attention due to their high -factors and ability to provide low-threshold near-UV lasing. However, a detailed understanding of the optical gain mechanisms in such structures has not yet been achieved. In this work, we study the mechanisms of stimulated emission (SE) in hexagonal ZnO microrods, demonstrating high-performance WGM lasing with thresholds down to 10-20 kW/cm and -factors up to ~3500. The observed SE with a maximum in the range of 3.11-3.17 eV at room temperature exhibits a characteristic redshift upon increasing photoexcitation intensity, which is often attributed to direct recombination in the inverted electron-hole plasma (EHP). We show that the main contribution to room-temperature SE in the microrods studied, at least for near-threshold excitation intensities, is made by inelastic exciton-electron scattering rather than EHP. The shape and perfection of crystals play an important role in the excitation of this emission. At lower temperatures, two competing gain mechanisms take place: exciton-electron scattering and two-phonon assisted exciton recombination. The latter forms emission with a maximum in the region near ~3.17 eV at room temperature without a significant spectral shift, which was observed only from weakly faceted ZnO microcrystals in this study.