Scientists at Los Alamos National Laboratory (Los Alamos, NM) have incorporated colloidal quantum dots (CQDs) into a new type of electrically pumped LED containing an integrated optical resonator, which also allows the device, when optically pumped, to function as a laser. The device, which emits at 618 nm with a quantum yield of about 80%, is a step toward mass-producible electrically pumped CQD lasers. This novel, dual-function device opens a path to versatile, easy-to-fabricate laser diodes—because the output wavelength can be tailored by changing the size of the CQDs, the technology can potentially result in lasers with wavelengths anywhere within a broad spectrum. Solution-processable CQD lasers can be produced in less-challenging lab and factory conditions than conventional semiconductor laser diodes, and could lead to devices that would benefit a number of emerging fields, including integrated photonics and other optical circuitry, lab-on-a-chip platforms, and wearable devices.
For the past two decades, the Los Alamos team has been working on fundamental and applied aspects of lasing devices based on semiconductor CQDs. The researchers have now successfully resolved several challenges on the path to commercially viable colloidal quantum dot technology, including the new LED/laser. In the device, they incorporated an optical resonator directly into the LED architecture without obstructing charge-carrier flows into the quantum-dot emitting layer. Further, by carefully designing the structure of their multilayered device, they could achieve good confinement of the emitted light within the ultrathin CQD medium of on the order of 50 nm, which is key to obtaining the lasing effect and, at the same time, allowing for efficient excitation of the CQDs by the electrical current. The final ingredient of the demonstration was homemade quantum dots perfected for lasing applications per recipes developed by the Los Alamos team over the years of research into the chemistry and physics of these nanostructures. Presently, the Los Alamos scientists are tackling the remaining challenge, which is boosting the current density to levels sufficient for obtaining population inversion. Reference: J. Roh et al., Nat. Commun. (2020); https://doi.org/10.1038/s41467-019-14014-3.
