An optical semiconductor device includes a substrate, a semiconductor multilayer which is formed on the substrate, and includes an optical functional layer, an insulating film formed on the semiconductor multilayer, and an electrode formed on a part of the insulating film. The insulating film covers the semiconductor multilayer except for a region in which the semiconductor multilayer and the electrode are electrically connected to each other. At least a part of a region of the insulating film that is overlapped with the electrode is thinner than a region of the insulating film that is not overlapped with the electrode.

A laser structure, including: a dielectric matrix formed of a first material; a laser source formed within the dielectric matrix and formed of a semiconductor material; and a plurality of side confining features formed within the dielectric matrix and extending parallel to and along a length of the laser source. The plurality of side confining features are formed of the semiconductor material.

A semiconductor optical element includes: a first conductivity type semiconductor substrate; and a laminated body disposed on the first conductivity type semiconductor substrate. The laminated body includes, in the following order from a side of the first conductivity type semiconductor substrate: a first conductivity type semiconductor layer; an active layer; a second conductivity type semiconductor layer; and a second conductivity type contact layer. The second conductivity type semiconductor layer includes: a carbon-doped semiconductor layer in which carbon is doped as a dopant in a compound semiconductor; and a group 2 element-doped semiconductor layer in which a group 2 element is doped as a dopant in a compound semiconductor. The carbon-doped semiconductor layer is disposed at a position closer to the active layer than the group 2 element-doped semiconductor layer.

A semiconductor laser element includes: a substrate having a projection at an upper face thereof; a first semiconductor layer; a light emission layer; a second semiconductor layer; and a low refractive index part having a refractive index lower than that of the first semiconductor layer. The second semiconductor layer has a ridge part for guiding laser light generated in the light emission layer. An angle between a side face of the ridge part and the waveguiding direction is larger than a limit angle defined by an effective refractive index on each of an inner side of the ridge part and an outer side of the ridge part. The low refractive index part is disposed between an active layer of the light emission layer and the projection of the substrate, and on the outer side of the side face at least where the width of the ridge part is small.

A semiconductor laser comprises a ridge formed on an n-type semiconductor substrate, a buried layer buried so as to cover both sides in an x-direction perpendicular to a y-direction, which is the direction in which the ridge extends. In a positive side of a z-direction that is the direction in which the ridge protrudes and the positive side of the buried layer in the z-direction, provided are a p-type second cladding layer, a p-type contact layer, a surface-side electrode that is connected to the p-type contact layer, and a semi-insulating layer that is formed on an outer edge separated from the ridge in the x-direction. The semi-insulating layer or the front surface-side electrode is formed on sides toward x-direction ends of the semiconductor laser on the positive side in the z-direction.

A semiconductor laser comprises a ridge formed on an n-type semiconductor substrate, a buried layer buried so as to cover both sides in an x-direction perpendicular to a y-direction, which is the direction in which the ridge extends. In a positive side of a z-direction that is the direction in which the ridge protrudes and the positive side of the buried layer in the z-direction, provided are a p-type second cladding layer, a p-type contact layer, a surface-side electrode that is connected to the p-type contact layer, and a semi-insulating layer that is formed on an outer edge separated from the ridge in the x-direction. The semi-insulating layer or the front surface-side electrode is formed on sides toward x-direction ends of the semiconductor laser on the positive side in the z-direction.

A laser structure, including: a dielectric matrix formed of a first material; a laser source formed within the dielectric matrix and formed of a semiconductor material; and a plurality of side confining features formed within the dielectric matrix and extending parallel to and along a length of the laser source. The plurality of side confining features are formed of the semiconductor material.

A semiconductor laser element includes a semiconductor laminated structure that has a substrate, an n type cladding layer disposed at a front surface side of the substrate, an active layer disposed at an opposite side of the n type cladding layer to the substrate, and p type cladding layers disposed at an opposite side of the active layer to the n type cladding layer. The active layer includes a quantum well layer having a tensile strain for generating TM mode oscillation and the n type cladding layer and the p type cladding layers are respectively constituted of AlGaAs layers.

An optical semiconductor device is provided with: a mesa in which a first conductivity type cladding layer, an active layer, and a second conductivity type first cladding layer having a second conductivity type are sequentially laminated on a surface of a first conductivity type substrate; a buried layer that buries both sides of the mesa with a top of the mesa being exposed; and a second conductivity type second cladding layer that buries the buried layer and the top of the mesa exposed from the buried layer, wherein the buried layer includes a layer doped with a semi-insulating material, and a boundary between the second conductivity type first cladding layer and the buried layer is inclined so that a width of the second conductivity-type first cladding layer becomes narrower toward the top of the mesa.

The upper surface of the semiconductor substrate has a slope descending from the projection in the second direction at an angle of 0-12° to a horizontal plane. The mesa stripe structure has an inclined surface with a slope ascending from the upper surface of the semiconductor substrate at an angle of 45-55° to the horizontal plane, the mesa stripe structure having an upright surface rising from the inclined surface at an angle of 85-95° to the horizontal plane. The buried layer is made from semiconductor with ruthenium doped therein and is in contact with the inclined surface and the upright surface. The inclined surface is as high as 80% or less of height from the upper surface of the semiconductor substrate to a lower surface of the quantum well layer and is as high as 0.3 μm or more.