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 eight-fold degenerate system, with a net modal gain in excess of 100 cm-1.