Hot-carrier effect and nanometer metal enabling Si-based mid-infrared detection beyond 5μm of wavelength

Detection of photons with energy below the bandgap or Schottky barrier height of silicon has been limited in the past. Here, we reveal an approach that harnesses hot carriers through diffusion over a very thin metal to achieve silicon-based mid-infrared detection. With strong localized surface plasmon resonance (LSPR) effect to enhance infrared absorption and diffusion across 10 nm metal in Schottky structure, the hot carriers can be effectively collected. Such mechanism leads to responsivity from 0.098 mA/W to 0.237 mA/W for the wavelengths between 2700 nm and 5300 nm, all corresponding to photon energy below Schottky barrier height. Our investigation further shows that inverted pyramidal structures could enhance LSPR and so the responsivity. In addition, this approach enables us to monitor high frequency optical signals up to 2.1 MHz. By harnessing hot carriers and enhancing LSPR, we have not only overcome previous limitations in silicon-based mid-infrared detection but also opened up new possibilities for advanced photonics and optoelectronics applications.