A backside illuminated sensor comprising a supporting substrate, a semiconductor layer which comprises a photodiode comprising a region of n-doped semiconductor provided at a first surface of the semiconductor layer, and a region of p-doped semiconductor, wherein a depletion region is formed between the region of n-doped semiconductor and the region of p-doped semiconductor, and a layer of p-doping protective material provided on a second surface of the semiconductor layer, wherein the first surface of the semiconductor layer is fixed to a surface of the supporting substrate.