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Continuous-wave lasing in colloidal quantum dot solids enabled by facet-selective epitaxy
- Publication Year :
- 2017
- Publisher :
- Nature Publishing Group, 2017.
-
Abstract
- By switching shell growth on and off on the (0001) facet of wurtzite CdSe cores to produce a built-in biaxial strain that lowers the optical gain threshold, we achieve continuous-wave lasing in colloidal quantum dot films. The electronic structure of colloidal quantum dots lends them a host of desirable optical properties, but they typically perform poorly as laser materials. Fengjia Fan et al. have developed a scheme for tuning this electronic structure in such a way that the barriers to laser action might be overcome. Specifically, they developed a synthesis strategy in which the shell of material encompassing the core of the quantum dot is asymmetric and compressive. This effectively squeezes the particle, thereby modifying the electronic structure to favour laser-like emissions. Colloidal quantum dots (CQDs) feature a low degeneracy of electronic states at the band edges compared with the corresponding bulk material1, as well as a narrow emission linewidth2,3. Unfortunately for potential laser applications, this degeneracy is incompletely lifted in the valence band, spreading the hole population among several states at room temperature4,5,6. This leads to increased optical gain thresholds, demanding high photoexcitation levels to achieve population inversion (more electrons in excited states than in ground states—the condition for optical gain). This, in turn, increases Auger recombination losses7, limiting the gain lifetime to sub-nanoseconds and preventing steady laser action8,9. State degeneracy also broadens the photoluminescence linewidth at the single-particle level10. Here we demonstrate a way to decrease the band-edge degeneracy and single-dot photoluminescence linewidth in CQDs by means of uniform biaxial strain. We have developed a synthetic strategy that we term facet-selective epitaxy: we first switch off, and then switch on, shell growth on the (0001) facet of wurtzite CdSe cores, producing asymmetric compressive shells that create built-in biaxial strain, while still maintaining excellent surface passivation (preventing defect formation, which otherwise would cause non-radiative recombination losses). Our synthesis spreads the excitonic fine structure uniformly and sufficiently broadly that it prevents valence-band-edge states from being thermally depopulated. We thereby reduce the optical gain threshold and demonstrate continuous-wave lasing from CQD solids, expanding the library of solution-processed materials11,12 that may be capable of continuous-wave lasing. The individual CQDs exhibit an ultra-narrow single-dot linewidth, and we successfully propagate this into the ensemble of CQDs.
- Subjects :
- Photoluminescence
Population
Nanotechnology
quantum dots
02 engineering and technology
Electronic structure
010402 general chemistry
Population inversion
01 natural sciences
Condensed Matter::Materials Science
Laser linewidth
LEDs and light sources
education
Physics
education.field_of_study
Multidisciplinary
business.industry
electronics
photonics and device physics
Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
021001 nanoscience & nanotechnology
0104 chemical sciences
Quantum dot laser
Quantum dot
Optoelectronics
0210 nano-technology
business
Lasing threshold
lasers
Subjects
Details
- Language :
- English
- Database :
- OpenAIRE
- Accession number :
- edsair.doi.dedup.....38738c6dda53851b4e1f3e5abbb5c624