Purcell enhancement in layered InSe on the Mie-resonant silicon nitride waveguide
Layered van der Waals semiconductors are promising active materials for nanoscale photonic and optoelectronic devices because their excitonic emission can be integrated with heterogeneous photonic architectures. For on-chip applications, this emission must be efficiently coupled to guided modes, while its recombination dynamics should be controlled by the local photonic environment. Although dielectric waveguides enable such integration, substantial control over radiative recombination generally requires resonant engineering of the local photonic density of states. Resonant dielectric nanostructures provide such control by modifying the photonic environment while preserving compatibility with guided-wave photonic architectures. Here, we demonstrate Purcell-enhanced excitonic emission from a thin InSe flake integrated with a Mie-resonant Si$_3$N$_4$ waveguide. The structure incorporates a resonant nanoparticle array with a resonance that overlaps the InSe PL band, thereby enhancing excitonic coupling to the guided mode. Optical spectroscopy confirms the designed resonance, while micro-photoluminescence measurements reveal enhanced and spectrally selective waveguide-coupled emission. Time-resolved photoluminescence measurements show a threefold shortening of the excitonic decay time relative to planar InSe. Analysis of the decay dynamics using a simple rate-equation model yields an effective Purcell factor of approximately 3 for the dominant out-of-plane excitonic emission channel. These results establish Mie-resonant dielectric waveguides as a compact platform for on-chip control of excitonic recombination in layered semiconductors.