Patent ID: 8519501

Claim:
A semiconductor light detecting element comprising: a semiconductor substrate of a first conductivity type and having opposed front and back surfaces; a first semiconductor layer of the first conductivity type on the front surface of the semiconductor substrate; a light absorbing layer on the first semiconductor layer; a second semiconductor layer on the light absorbing layer and comprising an impurity region of a second conductivity type having an interface with the light absorbing layer, wherein the impurity region forms a p-i-n structure with the first semiconductor layer and a part of the light absorbing layer that is disposed between the impurity region and the first semiconductor layer, the p-i-n structure defining a light-detecting region, light incident on the back surface of the semiconductor substrate and reaching the light detecting region is detected by the light detecting element, and the semiconductor substrate includes an air-filled groove having side walls, wherein the air-filled groove extends into the semiconductor substrate from the back surface of the semiconductor substrate, and surrounds the light-detecting region, when the semiconductor substrate in viewed in plan, perpendicular to the back surface, and the light-detecting region is projected onto the back surface of the semiconductor substrate, and the side walls reflect light obliquely incident on the back surface of the semiconductor substrate toward the light-detecting region; and a reflecting film, reflecting light that is incident on the back surface of the semiconductor substrate toward the light-detecting region, wherein the reflecting film is located on one of the side walls of the air-filled groove.