A photosite is formed in a semiconductor substrate and includes a photodiode confined in a direction orthogonal to the surface of the substrate. The photodiode includes a semiconductor zone for storing charge that is formed in an upper semiconductor region having a first conductivity type and includes a main well of a second conductivity type opposite the first conductivity type and laterally pinned in a first direction parallel to the surface of the substrate. The photodiode further includes an additional semiconductor zone including an additional well having the second conductivity type that is buried under and makes contact with the main well.