Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: A semiconductor optical device includes a semiconductor substrate and a stacked body formed by at least a first cladding layer, an active region and a second cladding layer; wherein both sides of the stacked body are buried by a burying layer formed by a semi-insulating semiconductor crystal; the burying layer includes a first layer that is placed adjacent to both sides of the stacked body and a second layer that is placed adjacent to the first layer; the first layer includes Ru as a dopant; composition of the second layer is different from the composition of the first layer, or a dopant of the second layer is different from the dopant of the first layer. The device can also be configured such that the width of the active region is smaller than the width of the cladding layers of the stacked body; and a Ru-doped semi-insulating layer is provided in a space between the burying layer and the active region in both sides of the active region.

Abstract: This semiconductor photodetector includes a photoabsorption layer, an n-type first semiconductor layer, and a p-type second semiconductor layer. The photoabsorption layer comprises an n-type first layer and a p-type second layer formed in contact with the first layer. The first semiconductor layer is arranged on the side of the first layer and has a shorter wavelength at a light absorption edge and a lower refractive index than in the photoabsorption layer. The second semiconductor layer is arranged on the side of the second layer and has a shorter wavelength at a light absorption edge and a lower refractive index than in the photoabsorption layer. When a predetermined reverse bias voltage is applied between the first and second semiconductor layers, the first layer is entirely depleted and the second layer is partially depleted.

Abstract: An optical functional device includes a semiconductor substrate, an optical functional layer provided on said semiconductor substrate and selected from the group consisting of a light emitting layer, a light absorbing layer, and an optical waveguide layer. The optical functional layer has a multi-quantum well layer. Preferably, the semiconductor substrate is a nonplanar semiconductor substrate having a ridge and two grooves adjacent said ridge, said ridge having a ridge width of from 1 to 10 .mu.m, a ridge height of from 1 .mu.m to 5 .mu.m, and a gap distance of from 1 .mu.m to 10 .mu.m. Such an optical functional device can be fabricated by growing, on a nonplanar semiconductor substrate having a specified dimension of the ridge, a strained multi-quantum well layer by metalorganic vapor phase epitaxy. Integrated optical device or circuit preferably includes an optical functional device on the nonplanar semiconductor substrate of a specified range of ridge shape factors.