The invention provides vertically-stacked photodiodes buried in a semiconductor material that are isolated and selectively contacted by deep trenches. One embodiment of the invention provides a pixel sensor comprising: a plurality of photosensitive elements formed in a substrate, each photosensitive element being adapted to generate photocharges in response to electromagnetic radiation; and a plurality of photocharge transfer devices, each photocharge transfer device being coupled to at least one of the plurality of photosensitive elements.