US Patent 7348608 Planar avalanche photodiode

A planar avalanche photodiode includes a small localized contact layer on the top of the device produced by either a diffusion or etching process and a semiconductor layer defining a lower contact area. A semiconductor multiplication layer is positioned between the two contact areas and a semiconductor absorption layer is positioned between the multiplication layer and the upper contact layer. The photodiode has a low capacitance and a low field near the edges of the semiconductor multiplication and absorption layers.