Experimental realization of purely excitonic lasing in ZnO microcrystals at room temperature: transition from exciton-exciton to exciton-electron scattering

TL;DR

This study demonstrates purely excitonic lasing in ZnO microcrystals at room temperature, revealing a transition from exciton-electron to exciton-exciton scattering as temperature decreases, and emphasizes the role of carrier diffusion.

Contribution

It provides experimental evidence that room-temperature lasing in ZnO microcrystals is driven by exciton-electron scattering, not exciton-exciton scattering as previously believed.

Findings

Pure excitonic lasing observed at room temperature in ZnO microcrystals.

Lasing mechanism shifts from exciton-electron to exciton-exciton scattering below 150 K.

Carrier diffusion significantly influences room-temperature excitonic lasing.

Abstract

Since the seminal observation of room-temperature laser emission from ZnO thin films and nanowires, numerous attempts have been carried out for detailed understanding of the lasing mechanism in ZnO. In spite of the extensive efforts performed over the last decades, the origin of optical gain at room temperature is still a matter of considerable discussion,. We show that ZnO microcrystals with a size of a few micrometers exhibit purely excitonic lasing at room temperature without showing any symptoms of electron-hole plasma emission. We then present the distinct experimental evidence that the room-temperature excitonic lasing is achieved not by exciton-exciton scattering, as has been generally believed, but by exciton-electron scattering. As the temperature is lowered below ~150 K, the lasing mechanism is shifted from the exciton-electron scattering to the exciton-exciton scattering. We also argue that the ease of carrier diffusion plays a significant role in showing room-temperature excitonic lasing.