Abstract: A novel process is disclosed in which an insulating layer is formed on a N type semiconductor substrate and an array of apertures is formed through the insulating layer to expose the substrate. A film of substantially intrinsic polycrystalline silicon is deposited over the insulating layer and the exposed substrate surfaces. A masking layer having a plurality of interconnecting members is formed photolithographically on the film, the members defining an array of openings in substantial registration with the apertures. A P type doping element, such as boron, is diffused laterally into the intrinsic film beneath each masking member and is simultaneously diffused into the substrate to form a plurality of PN junctions. The lateral diffusion is controlled so that the undoped regions underlying each of the masking elements have a width less than the width of the masking elements.