Patent ID: 7696593

Claim:
A semiconductor photo detecting element comprising: a PIN-type photo detecting element having a semiconductor substrate, a first semiconductor layer, a second semiconductor layer and a third semiconductor layer, the first through the third semiconductors layer being composed of InGaAs, the first semiconductor layer being provided on the semiconductor substrate, being lattice-matched to the semiconductor substrate, including a first conductivity type dopant, and having first band gap energy, the second semiconductor layer being provided on the first semiconductor layer, having the first band gap energy, and having a concentration of the first conductivity type dopant lower than that of the first semiconductor layer or being substantially undoped, the third semiconductor layer being provided on the second semiconductor layer, having the first band gap energy, and having a concentration of a second conductivity type dopant; a window semiconductor layer that is composed of InP, has second band gap energy larger than the first band gap energy at a light-incoming side with respect to the second semiconductor layer and has a thickness of 5 nm to 50 nm, the light passing through the window semiconductor layer; a protective semiconductor layer that is composed of InP, is provided on a side face of the first through the third semiconductor layers, has the second band gap energy, and has a thickness of more than 100 nm; and a passivation insulating layer being provided on the window semiconductor layer and the protective semiconductor layer.