Enhancing Responsivity in Silicon-Based Photodetectors for Mid-Infrared Sensing

In our recent investigation, we discovered Si-metal Schottky junction being able to detect mid-infrared spectrum under certain conditions. This work investigates the influence of the hot-carrier diffusion distance on such photodetectors to enhance responsivity in the mid-infrared (MIR) range. Due to the rapid decay characteristics, hot carriers disappear very fast. Thus we control the diffusion distance of hot carriers by varying the thickness of the metal thin film. A proper thickness of the metal boosts the responsivity for nearly 30-fold enhancement. Additionally, a mathematical model is employed to validate experimental results of hot carrier diffusing toward and leaping over the barrier. Furthermore, this research implements back-side illumination, bringing the excited carriers closer to the metal/semiconductor interface. The shortened diffusion distance of hot carriers leads to an increased responsivity in the photodetector within the MIR range. Consequently, it enables the detection of infrared (IR) signals with wavelengths of up to 4.26 mu m.