Photodiode structure having an enhanced blue color response

Abstract

Image detectors and scanners employing n.sup.+ - p photodiodes as the photosensitive element tend to have a low blue color response relative to the red color output due to loss of photogenerated carriers near the diode surface because of surface recombination, and because of a small minority carrier lifetime due to the high doping level of the n-region relative to the acceptor doping density of the substrate. The surface recombination and low lifetime cause loss of quantum efficiency at wavelengths less than 4200 A, which is the blue region. An improved photodiode is provided including a silicon p substrate, a junction formed by a phosphorous diffusion of low doping density, and a high dose of arsenic or phosphorous ion implantation to provide a shallow implant to create a built-in electric field which repels the photogenerated minority carriers away from the surface and towards the junction to be collected.