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

Abstract

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.

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Figure 1: Continuously graded core/shell CdSe/CdxZn1−xSe/ZnSe0.5S0.5 QDs (cg-QDs).
Figure 2: Auger recombination in cg-QDs and their lasing behaviours under optical excitation (room temperature).
Figure 3: cg-QD-LED employing a current-focusing architecture.
Figure 4: Double-band 1S and 1P electroluminescence (EL) from a cg-QD-LED (room temperature).
Figure 5: Optical gain in cg-QD-LED under electrical pumping (room temperature).

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Acknowledgements

V.I.K. and Y.-S.P. were supported by the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy. J.L. acknowledges support by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.

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J.L. synthesized the QDs, designed the ‘current-focusing’ device architecture, and fabricated and characterized the QD-LEDs. Y.-S.P. conducted spectroscopic studies of the QDs and measurements of their lasing characteristics. J.L. and Y.-S.P. provided equal contributions to this study. V.I.K. initiated the studies, developed the correlated electron–hole injection model, and wrote the manuscript with contributions from other co-authors.

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Correspondence to Victor I. Klimov.

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The authors declare no competing financial interests.

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Lim, J., Park, Y. & Klimov, V. Optical gain in colloidal quantum dots achieved with direct-current electrical pumping. Nature Mater 17, 42–49 (2018). https://doi.org/10.1038/nmat5011

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