There is disclosed a substrate including at least one photodetector, the photodetector having a first active area on a first surface of the substrate and a second active area on a second surface of the substrate, wherein the photodetector is provided with a conductive via electrically isolated from the substrate, said conductive via extending through the photodetector from the first surface of the substrate to the second surface of the substrate for connecting the first active area to the second surface of the substrate, the second surface providing electrical connections for the first and second active areas of the photodetector.