Integrated blue ZnSe/ZnS quantum dot lasers on a silicon nitride platform

On-chip blue lasers are essential for data storage, quantum photonics, optical communications and lab-on-chip sensing. Existing GaN-based devices deliver high performance but demand lattice-matched substrates, involve complex architectures and suffer from high optical losses in the visible range. Here we extend the CMOS-compatible fabrication methodology used to incorporate emitting colloidal quantum dots (QDs) with silicon nitride (SiN_x) platforms from proven red and green to blue lasers. Implementing QD design rules for optimal gain performance, we obtain blue-emitting ZnSe/ZnS QDs with gain metrics on par with established red and green QDs. After encapsulating QD films with an organic/inorganic bilayer, we demonstrate stable lasing under femtosecond and nanosecond pumping using different cavity designs. Such films, coated on low-loss SiN_x two-dimensional photonic crystal cavities, yield out-of-plane lasing between 425 and 445 nm, with quasi-continuous-wave thresholds of 7.5 kW cm^-2. In addition, in-plane, waveguide-coupled lasing is demonstrated by depositing ZnSe/ZnS QD films on top of a one-dimensional distributed feedback cavity. Our work underscores the potential of non-toxic, solution-processable ZnSe-based QDs for integrated blue photonics.