US Patent 9299865 Spad photodiode of high quantum efficiency

A SPAD-type photodiode has a semiconductor substrate with a light-receiving surface. A lattice formed of interlaced strips made of a first material covers the light receiving surface. The lattice includes lattice openings with lateral walls covered by a spacer made of a second material. Then first and second materials have different optical indices, and further each optical index is less than or equal to the substrate optical index. A pitch of the lattice is of the order of a magnitude of an operating wavelength of the photodiode. The first and second materials are transparent at that operating wavelength. The lattice is made of a conductive material electrically coupled to an electrical connection node (for example, a bias voltage node).