Reconfigurable Cavity-based Plasmonic Platform for Resonantly Enhanced Sub-bandgap Photodetection

Sub-bandgap photodetection based on plasmonic excitations represents a promising route for expanding the spectral range of photodetectors, enabling, for instance, silicon-based devices to be employed at telecom wavelengths. This approach harnesses internal photoemission, where hot carriers are generated via nonradiative plasmonic decay and are subsequently emitted from the metal to a semiconductor, yielding a photocurrent not spectrally limited by the bandgap. However, many schemes based on this approach suffer from low responsivities that hinders their uptake in real-world technologies. Here, we demonstrate a cavity-based platform for both enhancing the generated photocurrent and also providing a means for dynamic reconfiguration of the operating wavelength. The proposed device is composed of an optical cavity where one the mirrors is patterned with a nanoscale grating. Fabry-Perot resonances supported by the cavity provide resonant excitation of plasmonic modes at a metal/semiconductor interface, leading to augmented hot-carrier and photocurrent generation compared to the non-resonant case. By employing this cavity-grating geometry, we experimentally demonstrate a fivefold increase in photocurrent due to the presence of cavity resonances. Electromechanical reconfiguration of the photodetector cavity length is also achieved, illustrating dynamic control over the detection wavelength. This cavity-based architecture is compatible with a variety of plasmonic nanostructures, including nanoparticles and nanoantennas, thus providing a flexible means of significantly increasing photoresponse and hence bringing on-chip plasmonic hot-carrier technologies closer to realization for sub-bandgap photodetection, energy-harvesting and sensing.