Patent ID: 6885039

Claim:
A semiconductor photodetector comprising: (i) a semiconductor substrate; (ii) an optical waveguide having (a) a first conductivity type semiconductor layer formed on the semiconductor substrate, (b) an optical waveguide core layer formed on a partial area of the first conductivity type semiconductor layer, and (c) an upper cladding layer formed on the optical waveguide core layer; and (iii) an avalanche photodiode coupled to the optical waveguide, constructed by forming in sequence on another area of the first conductivity type semiconductor layer (a) a photo absorbing layer, (b) a heterobarrier relaxing layer, an underlying layer of a first conductivity type field dropping layer, (c) an overlying layer of the first conductivity type field dropping layer, (d) a carrier multiplying layer, and (e) a second conductivity type semiconductor layer; wherein a side surface of the underlying layer of the first conductivity type field dropping layer comes into contact with a side surface of the optical waveguide core layer, and a part of the overlying layer of the first conductivity type field dropping layer is formed on the optical waveguide core layer.