Optical detector

An optical detector comprising:

• a semiconductor base portion constituted by a first conductivity type semiconductor, having a first surface and a second surface facing the first surface, and provided with a projection projecting from the second surface;
• a first metal electrode layer provided on the first surface or the second surface of the semiconductor base portion;
• a semiconductor layer constituted by a second conductivity type semiconductor and having a first portion covering the second surface of the semiconductor base portion and second portions covering side surfaces of the projection;
• and
• second metal electrode layers provided in close contact with the semiconductor layer such that the projection and the second portions of the semiconductor layer are interposed therebetween,
• wherein an MIM resonator is constituted by the projection, the second portions of the semiconductor layer, and the second metal electrode layers between which the projection and the second portions of the semiconductor layer are interposed, and
• wherein a resonator length of the MIM resonator is a length in which a surface plasmon is excited by incident light having a wavelength longer than the wavelength of absorption edge of each of the semiconductor base portion and the semiconductor layer and a phonon is excited by an electric field formed by a resonance of the surface plasmon.