Processing of silicon UV-photodetectors

UV-enhanced photodetectors of both n+–p and p+–n type have been processed in silicon. Photodetectors of the p+–n type display a responsivity close to the theoretical limit with an antireflective coating of either thermally grown dry silicon dioxide or deposited oxide (TEOS), followed by a short wet oxidising step. This holds, irrespective of whether the detector window is doped by boron through ion implantation or diffusion from a solid source. However, for p+–n photodiodes with a TEOS-oxide in the as-deposited state the responsivity decreases substantially for wavelengths below 500 nm compared to the theoretical predictions. This is attributed to a high recombination velocity at the silicon dioxide/silicon interface, as supported by computer simulations of the detector performance. In contrast, n+–p photodiodes are found to be rather insensitive with respect to the properties of the silicon dioxide/silicon interface. These results provide the first experimental demonstration that high built in electric fields, caused by abrupt dopant profiles, can suppress the influence of a high interface carrier recombination velocity.