Liquid Semiconductor Lasers and Laser Diodes Based on Colloidal Quantum Dots

Colloidal quantum dots (QDs) are attractive materials for the implementation of solution-processed lasers, including both stand-alone and chip-integrated devices [1]. Their advantages include size-tunable emission wavelengths, low optical-gain thresholds, and high temperature stability of lasing characteristics. So far, all validated reports on colloidal QD lasing have used optically excited close-packed solid-state QD films. Two classes of QD lasers that have yet to be realized are liquid-state optically pumped devices and electrically pumped solid-state lasers (laser diodes). In both cases, the main obstacle is the very fast Auger recombination of optical-gain-active multicarrier states [2]. One consequence of the fast Auger decay is the existence of a minimum (critical) QD concentration required for lasing. Due to solubility limits, this concentration is difficult to achieve with liquid-state samples. Therefore, high-density solid-state films have been used in laser QD devices so far. The fast Auger delay also poses a serious problem when attempting to realize electrically pumped lasing. In particular, it requires the use of extremely high current densities for maintaining QDs in the inverted multicarrier state.
Here we describe how we overcome the problem of fast Auger recombination using novel type-(I+II) QDs, with which we implement a new optical gain mechanism based on stimulated emission of hybrid (direct/indirect) biexcitons with slow relaxation dynamics similar to charged excitons [3]. As a result, the type-(I+II) QDs exhibit long optical gain lifetimes (nanosecond time scales) while maintaining strong quantum confinement. We use our novel QDs to demonstrate new types of laser devices, including prototype solution-processed laser diodes [4] and broadly tunable dye-like liquid-state lasers [3].

[1] Y.-S. Park, J. Roh, B.T. Diroll, R.D. Schaller, V.I. Klimov, Colloidal quantum dot lasers, Nature Reviews Materials 6, 382-401 (2021).
[2] V.I. Klimov, A.A. Mikhailovsky, S. Xu, A. Malko, J.A. Hollingsworth, C.A. Leatherdale, H.J. Eisler, M.G. Bawendi, Optical gain and stimulated emission in nanocrystal quantum dots, Science 290, 314-317 (2000).
[3] D. Hahm, V. Pinchetti, C. Livache, N. Ahn, J. Noh, V.I. Klimov, Colloidal quantum dots enable tunable liquid-state lasers, Nat. Mater. in press (2024).
[4] N. Ahn, C. Livache, V. Pinchetti, H. Jung, H. Jin, D. Hahm, Y.-S. Park, V.I. Klimov, Electrically driven ASE from colloidal quantum dots, Nature 617, 79-85 (2023).