Previous research in infrared sensing mainly focused on narrow bandgap semiconductor materials, tunable bandgap two-dimensional (2D) materials. However, it is challenging to integrate them with silicon electronics due to lattice mismatch with silicon. To address this challenge, this work proposes a concept of infrared detection different from that of narrow bandgap semiconductors and 2D materials. In this study, thin metal/semiconductor Schottky devices were fabricated to realize mid-infrared light detection by collecting thermal signals generated by hot carriers with energy lower than the Schottky barrier. Experimental results demonstrate successful detection of mid-infrared light signals at wavelengths of 3.22 μm, 4.28 μm, and 4.83 μm, surpassing the cutoff wavelength corresponding to Schottky barrier. Such Schottky devices exhibit a maximum responsivity of 0.680 mA/W, which confirms their efficiency and application potential in application of mid-infrared optical detection.
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 4.26μm.
A Schottky infrared photodetector with dual mechanisms, where both photoelectric and photothermal current generation mechanisms coexist is presented. The dominant role of these mechanisms changes with surface passivation process. In the device without passivation process, the device exhibits high responsivity due to the presence of the photothermal effect but has slow rise and recovery times. However, after surface passivation treatment, the device characteristics are dominated by the photoelectric effect, showing a significantly faster response time, capable of detecting signal level changes within less than 80 ms, with a constant current difference between on and off states. This unique multifunctionality promotes the development of Schottky device capable of achieving multiple optical detection purposes
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