Patent ID: 7880197

Claim:
An avalanche photodiode formed by sequentially depositing an n-type electrode layer, an avalanche multiplication layer, an electric field control layer, a bandgap graded layer, an optical absorption layer and a p-type electrode layer, the optical absorption layer and the p-type electrode layer forming a mesa structure, the avalanche photodiode comprising: a buffer layer formed between the n-type electrode layer and the avalanche multiplication layer; and an n-type doping region being formed inside of said buffer layer and within an area defined by said mesa structure, as viewed from the mesa structure, being brought into contact with the n-type electrode layer, having a substantially trapezoidal shape in cross section, wherein the n-type doping region has a monotonically increasing concentration distribution both from the avalanche multiplication layer toward the n-type electrode layer and from the peripheral region towards the center within the n-type doping region.