NIR sensitivity enhancement by laser treatment for Si detectors

The light absorption coefficient of silicon is high in the short wavelengths, but much lower in the long wavelengths (longer than 900 nm). Thus it is necessary to use thicker silicon wafers to manufacture high-sensitivity light sensors for long wavelength applications. However, this imposes constraints on applied voltage, dark current, response speed, and cost. This then leads to limitations on device characteristics and possible applications. As an alternative to using thicker silicon wafers to enhance the NIR sensitivity of silicon photodiodes, we used an ultra-short pulse laser to form “black silicon” structures on the surface of silicon photodiodes. At 1064 nm, QE was improved from 25% to 72%. Future research will determine how this technology can also be applied to enhancing the NIR sensitivity of image sensors such as CCDs.