Patent ID: 7675130

Claim:
A waveguide photodetector detecting light incident on a light detecting end face, comprising: a substrate; and a layer stack structure on said substrate and including a semiconductor layer of a first conductivity type, an undoped semiconductor layer, and a semiconductor layer of a second conductivity type, stacked on one another in that order, said undoped semiconductor layer being not intentionally doped with any dopant impurity, wherein said undoped semiconductor layer includes at least two undoped light-absorbing layers in a stacked configuration and at least one undoped non-light-absorbing layer, each undoped non-light-absorbing layer being sandwiched by an adjacent pair of the undoped light-absorbing layers, said non-light-absorbing layers have a bandgap wavelength shorter than the wavelength of the incident light that is detected, and each of the non-light-absorbing layers is at least 150 nm thick.