A quantum cascade laser has a core region including a first injection layer, an active region, and a second injection layer. The active region includes a first well layer, a second well layer, a third well layer, a first barrier layer, and a second barrier layer. The first barrier layer is disposed between the first well layer and the second well layer and separates the first well layer from the second well layer. The second barrier layer is disposed between the second well layer and the third well layer and separates the second well layer from the third well layer. The first barrier layer has a thickness of 1.2 nm or less, and the second barrier layer has a thickness of 1.2 nm or less.

A semiconductor optical device may include a semiconductor substrate; a mesa stripe structure that extends in a stripe shape in a first direction on the semiconductor substrate and includes a contact layer on a top layer; an adjacent layer on the semiconductor substrate and adjacent to the mesa stripe structure in a second direction orthogonal to the first direction; a passivation film that covers at least a part of the adjacent layer; a resin layer on the passivation film; an electrode that is electrically connected to the contact layer and extends continuously from the contact layer to the resin layer; and an inorganic insulating film that extends continuously from the resin layer to the passivation film under the electrode, is spaced apart from the mesa stripe structure, and is completely interposed between the electrode and the resin layer.

A semiconductor optical device, in which a light emitting region and a modulator region are integrated, includes a first mesa disposed in the light emitting region, protruding in a direction that intersects a light propagation direction, and including an active layer, first and second buried layers disposed on the first mesa in a direction that intersects the light propagation direction and sequentially stacked in a direction in which the first mesa protrudes, a first semiconductor layer disposed on the first mesa and the second buried layer, a second mesa disposed in the modulator region and including a light absorption layer, and a third buried layer disposed on the second mesa. The first semiconductor layer and the first buried layer each have a first conductivity type. The second buried layer has a second conductivity type different from the first conductivity type, and the third buried layer is a semi-insulating semiconductor layer.

A method for manufacturing a monolithically integrated semiconductor optical integrated element comprising a DFB laser, an EA modulator, and a SOA disposed in a light emitting direction, comprising the step of forming a semiconductor wafer on which the elements are two-dimensionally arrayed and aligned the optical axes; cleaving the semiconductor wafer along a plane orthogonal to the light emitting direction to form a semiconductor bar including a plurality of the elements arranged one-dimensionally along a direction orthogonal to the light emitting direction such that the elements adjacent to each other share an identical cleavage end face as a light emission surface; inspecting the semiconductor bar by driving the SOA and the DFB laser through a connection wiring part together; and separating out the semiconductor bar after the inspection to cut the connection wiring part connecting the electrode of the SOA and the DFB laser to isolate from each other.

A semiconductor optical element has a mesa structure in which an active layer is embedded, and comprises a straight propagating section and a spot size converter section being such that a light confinement in the active layer is weaker than that of the straight propagating section, wherein in a same plane parallel to a layer surface of the active layer, an average value of a width of the mesa structure of the straight propagating section is smaller than a value of the width of the mesa structure at the emission facet of the spot size converter section, and at a top part of the mesa structure, an electrode is formed so that an electric current is injected in the active layer across the entire length of the straight propagating section and the spot size converter section.

To provide an optical semiconductor device having excellent long-term reliability, the optical semiconductor device includes: a substrate; a mesa structure provided on the substrate; a semiconductor burial layer provided in contact with two sides of the mesa structure; and an electrode containing Au, which is provided above the semiconductor burial layer. The mesa structure includes a first conductivity type semiconductor layer, a multiple-quantum well layer, and a second conductivity type semiconductor layer, which are stacked in the stated order from a substrate side. The semiconductor burial layer includes a first semi-insulating InP layer provided in contact with side portions of the mesa structure, a first anti-diffusion layer provided in contact with the first semi-insulating InP layer, and a second semi-insulating InP layer provided on the first anti-diffusion layer. The first anti-diffusion layer has an Au diffusion constant that is smaller than that of the first semi-insulating InP layer.

What is provided here are: a step of forming a first semiconductor layer on a base member; a step of forming a mask on the first semiconductor layer; a step of etching the first semiconductor layer by using the mask, to thereby form a semiconductor structure; a step of forming a second semiconductor layer in a region abutting on a side surface of the semiconductor structure, said second semiconductor layer having a convex portion abutting to the mask; a convex-portion removing step of removing the convex portion by supplying an etching gas thereto; and a regrown-layer forming step of supplying a material gas onto the semiconductor structure and the second semiconductor layer, to thereby form a regrown layer; wherein the convex-portion removing step and the regrown-layer forming step are executed in a same manufacturing apparatus.

A semiconductor optical element is configured to emit or absorb light and includes a lower structure that includes a multiple quantum well layer; an upper mesa structure that is disposed on the lower structure; a current injection structure that is disposed on the upper mesa structure, when seen from an optical axis of the emitted or absorbed light, a width of a portion of the current injection structure in contact with the upper mesa structure is smaller than a width of the upper mesa structure, the portion of the current injection structure in contact with the upper mesa structure consisting of InP, and an average refractive index of the upper mesa structure is higher than a refractive index of the InP forming the current injection structure; and an insulating film covering both side surfaces of the upper mesa structure and a part of an upper surface of the upper mesa structure.

A method of fabricating an optoelectronic component, performed on a multi-layered wafer disposed on a substrate. The method comprises the steps of: etching the multi-layered wafer, thereby defining a slab and a multi-layered ridge, the slab having an upper surface below the ridge and being located between the multi-layered ridge and the substrate; selectively epitaxially growing a III-V semiconductor cladding adjacent to a first and second sidewall of the ridge, the cladding layer extending from the upper surface of the slab along the first and second sidewalls, and thereby cladding an optically active waveguide within the multi-layered ridge; and providing a first and second electrical contact, which electrically connect to a layer of the multi-layered ridge and the slab respectively.

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.