Abstract: A semiconductor optical device includes a first semiconductor layer, and a diffraction grating disposed on the first semiconductor layer. The diffraction grating includes portions of a superlattice layer grown on the first semiconductor layer and including alternatingly arranged second semiconductor layers of a semiconductor material in which mass transport hardly occurs, during growth of other semiconductor layers and third semiconductor layers of a semiconductor material different from the material of the second semiconductor layers. The device includes a fourth semiconductor layer burying the diffraction grating. In this structure, since the second semiconductor layers are included in the diffraction grating, the shape of the diffraction grating is maintained during the vapor phase deposition of the fourth semiconductor layer. Therefore, the thickness, amplitude, and pitch of the diffraction grating that determine the optical coupling constant are controlled with high precision.

Abstract: An optical switch includes a semiconductor substrate having a surface, a ridge waveguide disposed on the surface of the semiconductor substrate and including an optical waveguide layer having an MQW structure, first and second cladding layers sandwiching the optical waveguide layer, and a switch disposed in a part of the ridge waveguide. A part of the MQW optical waveguide layer included in the switch is thicker than the other part of the optical waveguide layer, whereby the energy band gap of the optical waveguide layer of the switch is smaller than the energy band gap of the other part of the optical waveguide layer and larger than the energy of the signal light. Therefore, the absorption loss of the signal light traveling through the optical waveguide layer is reduced. Furthermore, since the variation in the refractive index of the switch when current is applied to the switch is increased, the ON/OFF ratio of the switch is increased.

Abstract: In a method of producing an infrared detector, a first conductivity type semiconductor layer, in which lattice vacancies acting as first conductivity type carriers are formed by evaporation of an element during annealing, is formed on a substrate and dopant impurities producing a second conductivity type are diffused in an annealing step from the impurity layer into the first conductivity type semiconductor layer to form pixel regions. During the diffusion, the surface of the first conductivity type compound semiconductor layer corresponding to non-pixel regions is exposed. In the regions of the first conductivity type semiconductor layer which becomes non-pixel regions, the first conductivity type carrier concentration increases due to the lattice vacancies generated by the evaporation of an element and, even when the dopant impurity is diffused into these regions, these regions remain first conductivity type regions.

Abstract: A photodetector includes a compound semiconductor substrate including first and second elements and having a first energy band gap, a first conductivity type compound semiconductor light absorbing layer including at least one of the first and second elements and having a second energy band gap narrower than the first energy band gap, a transition layer having an energy band gap at least as wide as the second energy band gap and no wider than the first energy band gap disposed between and contacting the substrate and the light absorbing layer, at least a first recess extending through the substrate and the transition layer to the light absorbing layer, a second conductivity type region disposed in the light absorbing layer at the first recess, a first electrode disposed in the first recess in contact with the second conductivity type region, and a second electrode disposed in contact with the first conductivity type light absorbing layer.