An avalanche photodiode sensor includes a photoelectric conversion region disposed in a substrate and that converts incident light into electric charge. The avalanche photodiode sensor includes a first region of a first conductivity type on the photoelectric conversion region, and a cathode disposed in the substrate adjacent to the first region and coupled to the photoelectric conversion region. The avalanche photodiode sensor includes an anode disposed in the substrate adjacent to the cathode, and a contact of the first conductivity type disposed in the substrate. An impurity concentration of the first region is different than an impurity concentration of the contact.