Patent ID: 7504672

Claim:
A photodetector comprising: a first region with a first doping concentration and a first bandgap; and a second region with a second doping concentration and a second bandgap, the second bandgap being larger than the first bandgap; wherein a received photon excites a carrier to a conduction band of the first region, and wherein a potential barrier which prevents the carrier from moving from the first region to the second region is removed by an applied voltage, whereby carriers can move from the first region to the second region; and wherein the second region is at least partially compositionally graded such that a portion of the second bandgap corresponding to the potential barrier increases away from the first region and towards the second region and is effectively flattened under reverse bias of the photodiode, and wherein the first region is a P region, the second region is a P− region, and further comprising a third region as an N+ region; and wherein the P− and N+ regions form a diode.