A semiconductor laser diode (LD) having an optical grating is disclosed. The LD includes a lower cladding layer that buries the optical grating, an active layer, and an upper cladding layer. The active layer has a multi-quantum well (MQW) structure of barrier layers and well layers alternately arranged. The MQW structure further includes intermediate layers between the barrier layers and the well layers. The intermediate layers have a lattice constant between that of the barrier layers and that of the well layers. Each intermediate layer has a thickness thinner than 1 nm.

A semiconductor optical device 1 includes an active layer 4 provided on a substrate 2, a clad layer 5 provided on the active layer 4, and a contact layer 7 provided on the clad layer 5. The contact layer 7 contains a first impurity and a second impurity different from the first impurity. A semiconductor light source includes the active layer 4 provided on the substrate 2, the clad layer 5 provided on the active layer 4, and the contact layer 7 provided on the clad layer 5. The contact layer 7 contains the first impurity and the second impurity different from the first impurity.

A semiconductor laser may include a substrate, a multi quantum well (MQW) active layer, and an electron stopper layer. The MQW active layer may include a quantum well that is tensile strained and a barrier that is compressively strained. The barrier may be formed from an aluminum gallium indium arsenide phosphide alloy having a first Al.sub.xGa.sub.yIn.sub.(1-x-y)As.sub.zP.sub.(1-z) composition. The electron stopper layer may include an aluminum gallium indium arsenide phosphide alloy having a second Al.sub.xGa.sub.yIn.sub.(1-x-y)As.sub.zP.sub.(1-z) composition.

A quantum cascade laser includes a laser structure including first and second end faces, the laser structure including a semiconductor laminate region and a first embedding semiconductor region. The laser structure includes first and second regions arranged in a direction of a first axis extending from the first to second end faces. Each of the first and second regions includes the semiconductor laminate region. The semiconductor laminate region of the first region has a first recess. The semiconductor laminate region of the second region has a semiconductor mesa. The first recess and the semiconductor mesa extend in the direction of the first axis, and are aligned with each other. The semiconductor mesa has an end face extending in a direction of a second axis intersecting the first axis. The first embedding semiconductor region is disposed in the first recess so as to embed the end face of the semiconductor mesa.

A semiconductor laser diode type of a buried-hetero structure (BH-LD) is disclosed. The LD provides a mesa, a first burying layer, and a second burying layer, where the burying layers are provided in respective sides of the mesa so as to expose a top of the mesa. The mesa includes a lower cladding layer, an active layer, and an upper cladding layer, where the cladding layers have conduction type opposite to each other and, combined with the burying layers, constitute a carrier confinement structure. The second burying layer has an even surface overlapping with an even surface of the first burying layer, and has a thickness in a portion of the even surface that is thinner than a thickness thereof in a portion except for the even surface.

A semiconductor laser diode (LD) having an optical grating is disclosed. The LD includes a lower cladding layer that buries the optical grating, an active layer, and an upper cladding layer. The active layer has the multi-quantum well (MQW) structure of barrier layers and well layers alternately arranged to each other. The MQW structure further includes intermediate layers between the barrier layers and the well layers, and have lattice constant between that of the barrier layer and that of the well layer. The inter mediate layer has a thickness thinner than 1 nm.

A method of manufacturing a semiconductor device includes a step of forming a mesa portion including an active layer above a substrate, and an n-type layer above the active layer, a step of forming a current confinement portion on left and right of the mesa portion, the current confinement portion including a p-type current blocking layer, an n-type current blocking layer above the p-type current blocking layer, and an i-type or p-type current blocking layer above the n-type current blocking layer, and a p-type doping step of diffusing p-type impurities into the i-type or p-type current blocking layer, an upper portion of the n-type current blocking layer, and left and right portions of the n-type layer to change the upper portion of the n-type current blocking layer and the left and right portions of the n-type layer to p-type semiconductors.

A light emitting device includes a light emitting waveguide layer including a first semiconductor portion and a second semiconductor portion having a conductive type different from the first semiconductor portion, and forming a pn junction with the first semiconductor portion, an electrode being provided to the second semiconductor portion on a side opposite to the first semiconductor portion and injecting an electric current into the pn junction, and at least one optical portion, wherein the light emitting waveguide layer has a longitudinal direction in a first direction, the light emitting waveguide layer generates, at the pn junction, light having an energy smaller than a band gap energy of the semiconductors constituting the first semiconductor portion and the second semiconductor portion, and causes the light being generated to resonate in the first direction, and the optical portion emits the resonating light to a second direction intersecting with the first direction.

A method of manufacturing an optical semiconductor device includes a step of forming semiconductor layers on the surface of an n-type InP substrate; an etching step of forming an active layer ridge by etching part of the semiconductor layers; a cleaning step of removing Si having adhered to the surface of the etched semiconductor layers while feeding a source gas for the crystal growth and an etching gas; and a crystal growth step of forming buried layers along both sidewalls of the active layer ridge at a processing temperature higher than that in the cleaning step, and the cleaning step is performed with the ridge being kept in shape.

Provided is an optical semiconductor device which has long-term reliability since a threshold current is small, and a relaxation oscillation frequency is high. An optical semiconductor device includes an InP semiconductor substrate, a lower mesa structure that is disposed above the InP semiconductor substrate, and includes a multiple quantum well layer, an upper mesa structure that is disposed on the lower mesa structure, and includes a cladding layer, a buried semiconductor layer that buries both side surfaces of the lower mesa structure, and an insulating film that covers both side surfaces of the upper mesa structure by being in contact with both side surfaces of the upper mesa structure, in which the lower mesa structure includes a first semiconductor layer, above the multiple quantum well layer, and the upper mesa structure includes a second semiconductor layer which is different from the cladding layer in composition, below the cladding layer.