Article

Towards zero-threshold optical gain using charged semiconductor quantum dots

  • Nature Nanotechnology 12, 11401147 (2017)
  • doi:10.1038/nnano.2017.189
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Abstract

Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain threshold due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. These measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons.

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Acknowledgements

Work on the synthesis of core/alloy/shell quantum dots and studies of Auger recombination in synthesized materials were supported by the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy. The studies of the effect of charging on quantum dot optical gain properties were supported by the Laboratory Directed Research and Development (LDRD) programme at Los Alamos National Laboratory (LANL). K.W. acknowledges support by a LANL Director's Postdoctoral Fellowship.

Author information

Author notes

    • Kaifeng Wu

    Present address: State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.

Affiliations

  1. Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    • Kaifeng Wu
    • , Young-Shin Park
    • , Jaehoon Lim
    •  & Victor I. Klimov
  2. Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87131, USA

    • Young-Shin Park

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Contributions

J.L. synthesized the quantum dots and conducted their microstructural characterization. K.W. conducted spectroscopic studies of the effect of charging on quantum dot optical properties. K.W. and Y.-S.P. conducted measurements of amplified spontaneous emission. K.W. and V.I.K. analysed the data and performed modelling of optical-gain performance of charged quantum dots. K.W., Y.-S.P. and V.I.K. performed theoretical modelling of lasing using charged quantum dots. K.W. and V.I.K. wrote the manuscript, with input from the other authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Victor I. Klimov.

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