Single-photon avalanche diode includes a central junction having a central p+ area and a deep-n well in contact with the central p+ area, a p-type guard ring disposed between the central junction and the deep-n well, and a shallow trench isolation separated from the central p+ area. Imaging apparatus includes a plurality of pixels, each pixel comprising a complementary metal-oxide-semiconductor-implemented single photon avalanche device and one or more signal converters electrically coupled thereto and configured to detect changes in output therefrom.