High-Transparency SWIR Electrode with Ultrathin Silver Film and High-Index Overlay for Advanced Infrared Applications

Abstract

Achieving high optical transparency in the short-wavelength infrared (SWIR) is essential for advancing infrared applications. Conventional transparent electrodes based on conducting oxides and ultrathin metals often have poor transparency in the SWIR due to their high optical density compared to the visible region. In this study, we present a SWIR-transparent electrode consisting of an ultrathin silver film with a high-refractive-index overlay. The overlay placed on the ultrathin metal film facilitates strong optical interference, achieving a transmittance of 86% at 1300 nm and a sheet resistance of 14 Omega/square. This performance is one of the highest performances reported for metal film-based electrodes to the SWIR, considering the higher extinction coefficient in the SWIR. Notably, the electrodes maintain high transparency across a wide range of incidence angles, with less than 10% deviation at 50 degrees. The direct integration of these transparent electrodes into silicon substrates enables the first-ever demonstration of SWIR-transparent silicon hot carrier photodetectors. The device demonstrated stable photocurrent generation and minimal optical interference, making it suitable for applications such as LiDAR, infrared imaging, and optical communication. Our approach offers a promising solution for advancing SWIR-transparent optoelectronics, contributing to the development of high-performance devices for diverse infrared applications.