Disruptive Optical Gain Metrics in the Green and Near-Infrared Spectrum Using Weakly Confined CdX (X=S,Se,Te) Quantum Dots

Nanostructured semiconductors, or quantum dots (QDs), are heavily investigated for their applications in light emission such as light emitting diodes and lasers. The premise of cost-effective solution processing of such devices based on nanocrystals has recently driven research towards electrically pumped population inversion in laser diode structures. Challenges however remain to achieve net light amplification in the cavity due to a balance between limited material gains and lossy electrical contacts. Further reductions in threshold current densities, mainly limited by the non-radiative cap of <i>ca.</i> 1 nanosecond on the gain lifetime, are also required to achieve stable operation. Finally, color tunability is limited to the red by the gain bandwidth of the red-emitting CdSe/CdS QDs or even core/shell nanoplatelets used.<br/>Here, we show that weakly confined charge carriers in <i>giant </i>CdX (X=S,Se,Te) quantum dots display disruptive optical gain metrics that could alleviate these remaining issues. Being active in the green and near-infrared part of the spectrum, their properties match and even outcompeting state-of-the-art colloidal materials in the red. Material gain coefficients up to 50.000 cm^-1 combined with a broad gain window of &gt;100 nm and gain lifetimes close to 3 ns are found. Gain thresholds of 9 uJ/cm2 are also on-par with the best performances reported so-far for nanomaterials. Invoking a model of stimulated emission based on bulk semiconductor physics, we are able to explain all of these remarkable gain metrics if a large band gap renormalization effect is invoked. Our results show that weakly confined nanomaterials are excellent gain materials, combining straightforward wet chemical synthesis and the promise of solution processability with beyond state-of-the-art gain metrics.