Colloidal Quantum Dot Infrared Lasers Featuring Sub‐Single‐Exciton Threshold and Very High Gain

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Abstract
The use of colloidal quantum dots (CQDs) as a gain medium in infrared laser devices has been underpinned by the need for high pumping intensities, very short gain lifetimes, and low gain coefficients. Here, PbS/PbSSe core/alloyed‐shell CQDs are employed as an infrared gain medium that results in highly suppressed Auger recombination with a lifetime of 485 ps, lowering the amplified spontaneous emission (ASE) threshold down to 300 µJ cm−2, and showing a record high net modal gain coefficient of 2180 cm−1. By doping these engineered core/shell CQDs up to nearly filling the first excited state, a significant reduction of optical gain threshold is demonstrated, measured by transient absorption, to an average‐exciton population‐per‐dot 〈Nth〉g of 0.45 due to bleaching of the ground state absorption. This in turn have led to a fivefold reduction in ASE threshold at 〈Nth〉ASE = 0.70 excitons‐per‐dot, associated with a gain lifetime of 280 ps. Finally, these heterostructured QDs are used to achieve near‐infrared lasing at 1670 nm at a pump fluences corresponding to sub‐single‐exciton‐per‐dot threshold (〈Nth〉Las = 0.87). This work brings infrared CQD lasing thresholds on par to their visible counterparts, and paves the way toward solution‐processed infrared laser diodes.
Funding Information
  • H2020 European Research Council (101002306)
  • Agencia Estatal de Investigación (CEX2019‐000910 [MCIN/AEI/10.13039/501100011033], PID2020‐112591RB‐I00/10.13039/501100011033, PDC2021‐120733‐I00, MCIN/AEI/10.13039/501100011033)

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