Patent ID: 7432537

Claim:
A two-terminal avalanche photodiode (APD) comprising: first and second electrode layers, one of said first and second electrode layers being an anode layer and the other of said first and second electrode layers being a cathode layer, an absorption layer between the first and second electrode layers, a first multiplying stage between the absorption layer and the first electrode layer, a second multiplying stage between the first multiplying stage and the first electrode layer, wherein the electrical potential across each stage is established by the selection of doping levels in the structure and the voltage applied across the first and second electrode layers only, so that more than one multiplying stage can be operated without making additional independent electrical contacts to the APD, and a carrier relaxation region between the first and second multiplying stages to which no direct external electrical contact is made, wherein the macroscopic field strength in the carrier relaxation region is lower than the macroscopic field strength in the first and second multiplying stages, and the carrier relaxation region is composed of an undoped semiconductor material having a fundamental band gap that is greater than or equal to the greatest fundamental band gap of semiconductor material in the first multiplying stage and is greater than or equal to the greatest fundamental band gap of semiconductor material in the second multiplying stage.