1. A photodetector comprising: a semiconductor substrate; a plurality of pixel regions, each pixel region comprising an optically sensitive layer over the substrate, wherein the optically sensitive layer employs an n-type semiconductor and is contacted using a deep-work-function metal having a work function deeper than 4.5 eV below vacuum; a pixel circuit for each pixel region, each pixel circuit comprising a charge store and a read out circuit; and circuitry to select the charge store of a plurality of adjacent pixel regions for simultaneous reading to a shared read out circuit.