Improvement of Infrared Detectors for Tissue Oximetry using Black Silicon Nanostructures

We present a nanostructured surface, made of dry etched black silicon, which lowers the reflectance for light incident at all angles. This surface is fabricated on infrared detectors used for tissue oximetry, where the detection of weak diffuse light signals is important. Monte Carlo simulations performed on a model of a neonatal head shows that approximately 60% of the injected light will be diffuse reflected. However, the change in diffuse reflected light due to the change in cerebral oxygenation is very low and the light will be completely isotropic scattered. The reflectance of the black silicon surface was measured for different angels of incident and was fund to be below 10% for angles of incident up to 70°. The quantum efficiency of detectors with the black silicon nanostructures was measured and compared to detectors with a simple anti-reflection coating. The result was an improvement in quantum efficiency for both normal incident light and light incident at 38°.