Back illuminated photo detector and optical receiver module having a center portion of an exposed contact portion located on an optical axis of light
Provided is a back illuminated photo detector enabling easy determination of whether or not the radius of a beam spot on a light absorption layer is an appropriate size. The back illuminated photo detector includes: a semiconductor substrate having a first surface for receiving light; a semiconductor layer that is laminated on a second surface and includes a light absorption layer; a passivation film so as to expose a contact portion that is part of an upper surface of the semiconductor layer; and an electrode that is in contact with the semiconductor layer in the contact portion, and has a reflectance lower than that of the passivation film. The contact portion includes a center portion located on an optical axis, and an area of the center portion is smaller than a design cross-sectional area of a beam spot.
1. A back illuminated photo detector, comprising:
a semiconductor substrate having a first surface for receiving light;
a semiconductor layer that is laminated on a second surface opposed to the first surface, and comprises a light absorption layer configured to absorb the light;
a passivation film formed on the semiconductor layer so as to expose a contact portion that is part of an upper surface of the semiconductor layer; and
an electrode that is in contact with the semiconductor layer in the contact portion, and has a reflectance of the light lower than a reflectance of the light of the passivation film,
wherein the contact portion at least comprises a center portion located on an optical axis of the light,
wherein an area of the center portion is smaller than a design cross-sectional area of a beam spot of the light.
2. The back illuminated photo detector according to claim 1 , wherein an area of the upper surface of the semiconductor layer is larger than the design cross-sectional area of the beam spot of the light.
3. The back illuminated photo detector according to claim 1 , wherein the area of the center portion is equal to or smaller than 36% of an area of the upper surface of the semiconductor layer.
4. The back illuminated photo detector according to claim 1 , wherein the area of the center portion is equal to or larger than 1% of an area of the upper surface of the semiconductor layer.
5. The back illuminated photo detector according to claim 1 , wherein the contact portion comprises a peripheral portion surrounding the center portion while being separated from the center portion.
6. An optical receiver module, comprising:
the back illuminated photo detector of claim 1 ;
a collective lens arranged on the first surface side of the back illuminated photo detector; and
a package including the back illuminated photo detector and the collective lens.