Optical gain in colloidal quantum dots achieved with direct-current electrical pumping

• Published in: Nature materials 2018-01, Vol.17 (1), p.42-49
• Main Authors: Lim, Jaehoon, Park, Young-Shin, Klimov, Victor I.
• Format: Article
• Language: English
• Subjects: 639/624/1020; 639/925/927/1021; Augers; Biomaterials; Colloid chemistry; Condensed Matter Physics; Electroluminescence; Injection; Lasing; Materials Science; Nanocrystals; Nanotechnology; Optical and Electronic Materials; Optical pumping; Population inversion; Quantitative analysis; Quantum dots; Semiconductor lasers; Wavelengths
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat5011

Chemically synthesized semiconductor quantum dots (QDs) can potentially enable solution-processable laser diodes with a wide range of operational wavelengths, yet demonstrations of lasing from the QDs are still at the laboratory stage. An important challenge—realization of lasing with electrical injection—remains unresolved, largely due to fast nonradiative Auger recombination of multicarrier states that represent gain-active species in the QDs. Here we present population inversion and optical gain in colloidal nanocrystals realized with direct-current electrical pumping. Using continuously graded QDs, we achieve a considerable suppression of Auger decay such that it can be outpaced by electrical injection. Further, we apply a special current-focusing device architecture, which allows us to produce high current densities ( j ) up to ∼18 A cm −2 without damaging either the QDs or the injection layers. The quantitative analysis of electroluminescence and current-modulated transmission spectra indicates that with j = 3–4 A cm −2 we achieve the population inversion of the band-edge states. Core/shell type-I semiconductor nanocrystals with compositionally graded shell and embedded in a current-focusing device architecture reach population inversion, a condition required for lasing, when excited with direct current.