Semiconductor light receiving element

A semiconductor light receiving element including a light absorption region formed in a vicinity of a main surface of a semiconductor substrate transparent to an incident light, an incident region set concentrically with the light absorption region and larger than the light absorption region, and a revolving paraboloid shaped concave reflecting portion provided on a back surface opposite to the main surface of the semiconductor substrate and capable of reflecting incident light incident on the incident region from a side of the main surface of the semiconductor substrate toward the light absorbing region;

• wherein,
• when a radius of curvature of a partial spherical surface approximating a revolving paraboloid shape of the concave reflecting portion is R, a diameter of the incident region is B, a distance in the semiconductor substrate between the light absorbing region and the concave reflecting portion is W, and a diameter of the light absorbing region is P, then the radius of curvature R satisfies a condition of R≤2BW/(B−P) in order to avoid reduction of a coupling efficiency, and satisfies a condition of R≥2BW/(B−P/2) in order to avoid a space charge effect.