Patent ID: 8101971

Claim:
A photodiode comprising: a first ohmic contact of a first conductivity type; an InP or GaAs substrate of said first conductivity type, etched out from the backside so as to avoid absorption of incident light from the backside into said substrate; at least one semiconductor electric-field buffer layer of said first conductivity type formed at said substrate; wherein said at least one buffer layer is either a single highly doped buffer layer, or a plurality of buffer layers ordered in descending order of dopant concentration, such that the buffer layer adjacent to said substrate has the highest concentration of dopants of all the buffer layers; at least one InGaAs absorption layer formed at said at least one buffer layer; at least one spacer layer formed at said at least one absorption layer and covering the entire said at least one absorption layer to avoid dopant diffusion into said at least one absorption layer; at least one highly doped In-based ohmic contact layer of a second conductivity type opposite to said first conductivity type formed at said at least one spacer layer; and a second ohmic contact of said second conductivity type connected to said at least one contact layer; wherein said first ohmic contact is connected to said substrate or said at least one buffer layer; and wherein the thickness of said at least one buffer layer is evenly formed and thin enough to reduce the light absorption and diffusion induced current, and to distribute an electrical field uniformly over the incident surface of said substrate.