Semiconductor light receiving element

1. A semiconductor light receiving element of back-illuminated type comprising a light absorbing portion provided in a vicinity of a main surface of a semiconductor substrate transparent to an incident light, and a first convex lens portion having a larger diameter than the light absorbing portion and having a radius of curvature R 1 provided on a back surface of the semiconductor substrate opposite to the main surface, in which a center of the light absorbing portion is located on an optical axis of the first convex lens portion; wherein

in a central portion of the first convex lens portion, provided is a second convex lens portion having a common optical axis to the first convex lens portion, a smaller diameter than the light absorbing portion, and a curvature radius R 2 smaller than the curvature radius R 1 ,

the second convex lens portion has a focal point between the second convex lens portion and the light absorbing portion, thereby diffusing light incident on the second convex lens portion from the focal point toward the light absorbing portion,

based on a distance L from an emission point of the incident light to the second convex lens portion, a divergence angle θ of the incident light, a diameter D of the light absorbing portion, and a distance H between the second convex lens portion and the light absorbing portion, the radius of curvature R 2 of the second convex lens portion is set such that all of the incident light incident on the second convex lens portion is incident on the light absorbing portion, and

when a refractive index of the semiconductor substrate with respect to air is n, then the radius of curvature R 1 of the first convex lens portion satisfies a relation of (n−1)/(1/L+n/H)<R1<n−1)/(n/H).

2. The semiconductor light receiving element according to claim 1 , wherein the semiconductor substrate is made of an InP substrate.

3. A semiconductor light receiving element of back-illuminated type comprising a light absorbing portion provided in a vicinity of a main surface of a semiconductor substrate transparent to an incident light, and a first convex lens portion having a larger diameter than the light absorbing portion and having a radius of curvature R 1 provided on a back surface of the semiconductor substrate opposite to the main surface, in which a center of the light absorbing portion is located on an optical axis of the first convex lens portion; wherein

formed directly on a central portion of a convex surface of the first convex lens portion is a second convex lens portion having a common optical axis to the first convex lens portion, a smaller diameter than the light absorbing portion, and a curvature radius R 2 smaller than the curvature radius R 1 ,

the radius of curvature R 2 of the second convex lens portion is set such that all of the incident light incident on the second convex lens portion is incident on the light absorbing portion, and

the second convex lens portion has a focal point spaced from the first convex lens portion and situated between the second convex lens portion and the light absorbing portion, thereby diffusing light incident on the second convex lens portion from the focal point toward the light absorbing portion.

4. The semiconductor light receiving element according to claim 3 , wherein the semiconductor substrate is made of an InP substrate.