US Patent 7432537 Avalanche photodiode structure

An avalanche photodiode (APD) includes an anode layer, a cathode layer, an absorption layer between the anode layer and the cathode layer, a first multiplying stage between the absorption layer and the cathode layer, a second multiplying stage between the first multiplying stage and the cathode layer, and a carrier relaxation region between the first and second multiplying stages. Each multiplying stage includes, in the direction of drift of electrons, a first layer that is doped with acceptors, a second layer that is substantially undoped, a third layer that is doped with acceptors, a fourth layer that is substantially undoped, and a fifth layer that is doped with donors.