Patent ID: 7893460

Claim:
A semiconductor light detecting element comprising: a semiconductor substrate having a bandgap energy, a first major surface, and a second major surface opposite said first major surface; a first light reflective structure, a light absorptive layer, a phase adjusting layer, and a second light reflective structure, sequentially disposed, from said semiconductor substrate, on said first major surface of said semiconductor substrate; and an anti-reflection film on said second major surface of said semiconductor substrate, wherein said first light reflective structure includes a multilayer light reflective structure comprising laminated semiconductor layers having different refractive indices, each semiconductor layer having a respective optical thickness of nλ/4, wherein n is an odd positive integer and λ is the wavelength of incident light detected by said semiconductor light detecting element, said light absorptive layer has a band gap energy smaller than the band gap energy of said semiconductor substrate, said phase adjusting layer has a band gap energy larger than the band gap energy of said light absorptive layer, said first light reflective structure contacts said light absorptive layer without intervention of other layers, said first light reflective structure contacts said first major surface of said semiconductor substrate without intervention of other layers, said second light reflective structure contacts said phase adjusting layer without intervention of other layers, and said phase adjusting layer contacts said light absorptive layer without intervention of other layers, wherein said first and second light reflective structures, sandwiching said light absorptive layer and said phase adjusting layer, establish only a single resonator in which the incident light detected by said semiconductor light detecting element reciprocates between said first and second light reflective structures.