Single-Exciton Gain and Stimulated Emission Across the Infrared Telecom Band from Robust Heavily Doped PbS Colloidal Quantum Dots

Abstract

Materials with optical gain in the infrared are of paramount importance for optical communications, medical diagnostics and silicon photonics. The current technology is based either on costly III-V semiconductors that are not monolithic to silicon CMOS technology or Er-doped fiber technology that does not make use of the full fiber transparency window. Colloidal quantum dots (CQD) offer a unique opportunity as an optical gain medium in view of their tunable bandgap, solution processability and CMOS compatibility. The 8-fold degeneracy of infrared CQDs based on Pb-chalcogenides has hindered the demonstration of low-threshold optical gain and lasing, at room temperature. We demonstrate room-temperature, infrared, size-tunable, band-edge stimulated emission with linewidth of ~14 meV. Leveraging robust electronic doping and charge-exciton interactions in PbS CQD thin films, we reach gain threshold at the single exciton regime representing a four-fold reduction from the theoretical limit of an eightfold degenerate system, with a net modal gain in excess of 100 cm -1 .

Electrically Pumped QD Light Emission from LEDs to Lasers

“…47 Both approaches, however, involve low oscillator strength transitions that sacrifice material gain to obtain a long inverted state lifetime and a low gain threshold. More recently, electrochemical doping of CdSe/CdS or chemical doping of PbS CQDs was successfully explored as a method to reduce the gain threshold, 48,49 yet stimulated emission still involves a multi-exciton state prone to rapid Auger recombination. Finally, theoretical considerations highlighted the possible impact of exciton-phonon coupling, which can yield single exciton gain when combined with biexci- ton repulsion, not unlike organic dyes.…”

Low‐Threshold, Highly Stable Colloidal Quantum Dot Short‐Wave Infrared Laser enabled by Suppression of Trap‐Assisted Auger Recombination

“…Semiconductor colloidal quantum dots (CQDs) have shown great promise as gain materials for solution-processed lasers, ranging from the visible [1][2][3][4][5] to the infrared. [6,7] However, light amplification in CQDs is severely hindered by intrinsic multi-highly stable single-mode lasing emission in the infrared owing to suppression of the Auger recombination and reduction of self-absorption losses in the gain medium. To our knowledge this constitutes the first demonstration of suppressing Auger recombination in CQD solids by engineering at the suprananocrystalline level.…”

“…Yet, those were achieved under high optical pump intensities, where the ASE and lasing thresholds for neutral PbS QD films is in the range of 800-1500 μJ cm -2 . [6] Moreover, the reported biexciton Auger lifetimes for PbS QDs film is ≈200 ps, [6] which is an order of magnitude faster than engineered CdSebased QDs. [9,11,15] The high ASE and lasing thresholds in PbS QD films are attributed to very fast Auger process and high degeneracy of Pb-chalcogenide QDs (eightfold).The photoexcited carriers in QDs can be captured by midgap surface trap-states, resulting in long-lived net charges.…”

Azobenzenes as Light-Activable Carrier Density Switches in Nanocrystals

“…Nanocrystals (NCs) appear as an important building block for solution-processed optoelectronic devices 1,2 such as light emitting diodes, 3 solar cells 4 and infrared (IR) sensors. 5,6 In this quest, the doping control becomes of utmost interest: it is critical for the design of p-n junctions, 7 to reduce lasing threshold 8 or to induce intraband absorption in the mid infrared. 9,10 Doping of NCs can be obtained from various methods: [11][12][13] introduction of extrinsic impurities [14][15][16] within the NCs or within the array of nanocrystals, non-stoichiometry of the material (Cu2-xS, 17 (Bi;Sb)2Te3, HgSe 18,19 ), metal functionalization, 20,21 functionalization by redox molecules 22,23 or surface dipole functionalization.…”