Recent Progress Towards Colloidal Quantum Dot Laser Diodes

Due to high emission efficiencies and size-controlled emission wavelengths, colloidal quantum dots (QDs) are attractive materials for the realization of solution-processable laser diodes [1, 2]. In addition to facile spectral tunability, QD gain media benefit from a wide separation between their atomic-like states, which inhibits thermal depopulation of the band-edge ‘emitting’ levels and thereby reduces lasing thresholds and improves temperature stability [3]. Despite these advantageous features, colloidal QD lasers are yet to reach the stage of technologically viable devices. A primary obstacle is nonradiative Auger recombination, which leads to very fast relaxation of optical gain [4]. This represents an especially serious challenge in the case of inherently slow electrical pumping when multiexciton states, required for optical gain, are generated via step-by-step injection of individual carriers. Another complication is poor stability of QD solids under high current densities needed to enact the lasing effect. Recently, these challenges have been successfully tackled via novel approaches to Auger decay engineering and special strategies for boosting current densities to ultrahigh values of ~1,000 A cm^-2[5]. These advances have brought the QD lasing community very close to its ultimate objective, which is the realization of a QD laser diode (QLD). In this presentation, I will overview the principles of light amplification with colloidal QDs, assess the status of the QD lasing field, examine the remaining challenges on a path to a QLD, and, finally, discuss practical strategies for attaining electrically pumped QD lasing.<br/> <br/>[1] Y.-S. Park, J. Roh, B.T. Diroll, R.D. Schaller, V.I. Klimov, Colloidal quantum dot lasers, Nature Reviews Materials <b>6,</b> 382 (2021).<br/>[2] H. Jung, N. Ahn, V.I. Klimov, Prospects and challenges of colloidal quantum dot laser diodes, Nature Photonics <b>15</b>, 643 (2021).<br/>[3] Y. Arakawa, H. Sakaki, Multidimensional Quantum Well Laser and Temperature-Dependence of Its Threshold Current, Appl. Phys. Lett. <b>40, </b>939 (1982).<br/>[4] V.I. Klimov, A.A. Mikhailovsky, A. Malko, J.A. Hollingsworth, C.A. Leatherdale, H.J. Eisler, M.G. Bawendi, Optical gain and stimulated emission in nanocrystal quantum dots, Science <b>290, </b>314 (2000).<br/>[5] J. Lim, Y.-S. Park, V.I. Klimov, Optical Gain in Colloidal Quantum Dots Achieved by Direct-Current Charge Injection, Nature Materials <b>17</b>, 42 (2018).