SWIR-transparent silicon hot-carrier photodetector for unobstructed real-time laser power monitoring

Optically transparent photodetectors are becoming essential components in next-generation photonic technologies such as augmented reality and light-field imaging. While transparent photodetectors have been extensively developed for the visible spectrum, extending this capability to the short-wavelength infrared (SWIR) regime remains a significant challenge. This is primarily due to the lack of suitable transparent electrodes and the difficulty in minimizing the thickness of light-absorbing layers. In this work, we demonstrate an SWIR-transparent silicon hot-carrier photodetector, enabled by an ultrathin silver film topped with a high-refractive-index overlayer, serving as a transparent electrode. The electrode design exploits destructive interference to minimize reflection, achieving an 86% transmittance at 1300 nm and a normalized transmittance of 123% relative to a silicon substrate. Integrating this electrode into a silicon substrate forms a metal–silicon Schottky junction for SWIR photon detection through hot-carrier injection, with photon absorption confined to a sub-10 nm metal layer. By leveraging the optical transparency of our photodetector, we demonstrate a laser power monitoring strategy that enables real-time optical power measurements without compromising the spatial profile of the laser beam and altering its optical path. This work paves the way for compact, streamlined designs in applications such as optical data transmission and light detection and ranging (LiDAR), where continuous laser power monitoring is crucial.