Colloidal quantum well light-emitting waveguides

Abstract

Micro/nanoscale semiconductor light-emitting devices of colloidal nanocrystals offer low-cost solutions while delivering high performance in ambient lighting systems, displays, and photonic circuits. Colloidal quantum wells (CQWs) are excellent candidates as active materials for these optoelectronic devices owing to their superior properties including suppressed Auger recombination, large absorption cross-section, and narrow emission linewidth. In this thesis, as our first study, we proposed and demonstrated dual-color lasing using heterostructures of CQWs as the gain media in an all-solution-processed dual-color optical cavity for the first time. Here, a multilayered waveguide architecture consisting of green- and red-emitting CQWs, separated with a transparent low refractive index colloidal spacing layer of silica nanoparticles (NPs) suppressing otherwise detrimental nonradiative energy transfer between them, enabled amplified spontaneous emission (ASE) simultaneously in two colors at the threshold level of ~17 µJ/cm2 . We further adapted this multilayer waveguide configuration to a whispering-gallery-mode (WGM) cavity by fabricating a microdisk structure directly out of these layered CQWs-NPs-CQWs colloids. The resulting device showed dual-color multimode lasing both at 569 and 648 nm at the same time with the threshold of ~106 µJ/cm2 . Then, as the second study of this thesis, we developed a colloidal waveguide light-emitting diode (LED) structure of CQWs that changes the direction of light from the surface to the edge of the device by combining the active CQW region with a slit-shaped waveguide architecture that confines the light within the emissive layer and guides it through the lateral axis. Driving this LED waveguide of 900 µm in length by 150 µm in width at a current density level of 5.6 A/cm2 , we observed the output emission reached a luminance level of ~20,400 cd/m2 . These unique waveguiding architectures integrated into the light emitting devices of CQWs hold great promise for on-chip photonic applications including CQW dual-color excitation for biological imaging and CQW LED-based photonic integrated circuits.