Further Step to Quantum Dot Lasers

Los Alamos scientists have incor­porated meticulously engineered colloidal quantum dots into a new type of light emitting diodes containing an integrated optical resonator, which allows them to function as lasers. These novel, dual-function devices clear the path towards versatile, manu­facturing-friendly laser diodes. The technology can poten­tially revo­lutionize numerous fields from photonics and optoelectronics to chemical sensing and medical diagnostics.

Colloidal quantum dots operating in LED mode. (Source: LANL)

“This latest break­through along with other recent advances in quantum dot chemistry and device engineering that we have achieved suggest that laser diodes assembled from solution may soon become a reality,” said Victor Klimov, head of the quantum dot group at Los Alamos National Labora­tory. “Quantum dot displays and television sets are already available as commercial products. The colloidal quantum dot lasers seem to be next in line.”

Colloidal quantum dot lasers can be manufactured using cheaper, simpler methods than modern semiconductor laser diodes that require sophis­ticated, vacuum-based, layer-by-layer deposition techniques. Solution-processable lasers can be produced in less-challenging lab and factory conditions, and could lead to devices that would benefit a number of emerging fields including inte­grated photonic circuits, optical cir­cuitry, lab-on-a-chip platforms, and wearable devices.

For the past two decades, the Los Alamos quantum dot team has been working on fundamental and applied aspects of lasing devices based on semi­conductor nanocrystals prepared via colloidal chemistry. These colloidal quantum dots can be easily processed from their native solution environment  to create various optical, electronic, and optoelectronic devices. Further­more, they can be size-tuned for lasing appli­cations to produce colors not accessible with existing semi­conductor laser diodes.

Now, the Los Alamos researchers success­fully resolved several challenges on the path to commercially viable colloidal quantum dot tech­nology. In particular they demons­trated an operational LED, which also functioned as an optically-pumped, low-threshold laser. To achieve these behaviors, 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 quantum dot medium on the order of 50 nanometers across.

This is key to obtaining the lasing effect and, at the same time, allowing for efficient exci­tation of the quantum dots by the electrical current. The final ingredient of this successful demons­tration was unique, home-made quantum dots perfected for lasing appli­cations per recipes developed by the team over the years of research into the chemistry and physics of these nano­structures. Presently, the scientists are tackling the remaining challenge, which is boosting the current density to levels sufficient for obtaining popu­lation inversion – the regime when the quantum dot active medium turns into a light amplifier. (Source: LANL)

Reference: J. Roh et al.: Optically pumped colloidal-quantum-dot lasing in LED-like devices with an integrated optical cavity, Nat. Commun. 11, 271 (2020); DOI: 10.1038/s41467-019-14014-3

Link: Chemistry Division, Los Alamos National Laboratory, Los Alamos, USA

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