1. Effect of size and shape on the excitonic stimulated emission process in ZnO microstructures
- Author
-
Takashi Uchino and Ryosuke Matsuzaki
- Subjects
Materials science ,Photoluminescence ,Condensed Matter::Other ,Scattering ,Exciton ,Wide-bandgap semiconductor ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Molecular physics ,Grain size ,law.invention ,Condensed Matter::Materials Science ,law ,0103 physical sciences ,Stimulated emission ,010306 general physics ,0210 nano-technology ,Lasing threshold - Abstract
There has been some (partly controversial) discussion about the role of excitons in room-temperature laser emission of ZnO. Recently, we have demonstrated from temperature and excitation-density-dependent photoluminescence measurements on a ZnO film consisting of well crystallized micrometer-sized grains that the mechanism of optical gain at temperatures below ∼150 K is the exciton-exciton (ex-ex) scattering, whereas at temperatures from ∼150 K to room temperature, the gain results from the exciton-electron (ex-el) scattering without any contribution from electron-hole plasma lasing [R. Matsuzaki et al., Phys. Rev. B 96, 125306 (2017)]. However, the mechanism of optical feedback inside these ZnO microstructures is not fully understood. In this work, we investigate the emission properties of various ZnO microcrystals with different size and shape in the temperature region from 3 to 300 K using a nanosecond pulsed laser as an excitation source. We found that room temperature stimulated emission is observed only from the sphere-like ZnO particles with the size of a few micrometers in diameter. We also found the temperature-induced transition between ex-ex and ex-el scattering processes at a temperature of ∼150 K, similar to the case of the ZnO film consisting of micrometer-sized grains reported previously. The close similarity observed between the two different types of ZnO microstructures allows us to deduce that the temperature-dependent excitonic stimulated emission characteristics are common in micrometer-sized ZnO crystals with a low-loss feedback mechanism.
- Published
- 2018