An optical waveguide structure includes a lower cladding layer positioned on a substrate; an optical guide layer positioned on the lower cladding layer; an upper cladding layer positioned on the optical guide layer; and a heater positioned on the upper cladding layer. The lower cladding layer, the optical guide layer, and the upper cladding layer constitute a mesa structure. The optical guide layer has a lower thermal conductivity than the upper cladding layer. An equation W.sub.wgW.sub.mesa3W.sub.wg is satisfied, wherein W.sub.mesa represents a mesa width of the mesa structure, and W.sub.wg represents a width of the optical guide layer. The optical guide layer occupies one-third or more of the mesa width in a width direction of the mesa structure.

A distributed feedback laser, including: a ridge waveguide; two upper electrodes disposed on two sides of the ridge waveguide, respectively; two lower electrodes disposed on two sides of the upper electrodes, respectively; a substrate; a second waveguide cladding layer; an active layer; and a first waveguide cladding layer. The first waveguide cladding layer is n-doped and includes a conductive layer and a refractive layer disposed on the conductive layer. The refractive index of the refractive layer is greater than the refractive index of the active layer. The ridge waveguide includes a ridge region formed by a middle part of the refractive layer. The ridge region includes a surface provided with Bragg gratings. Two grooves are formed between the ridge waveguide and the upper electrodes. The conductive layer is connected to the upper electrodes. The second waveguide cladding layer includes one or more current restricted areas.

Semiconductor Quantum Cascade Lasers (QCLs), in particular mid-IR lasers emitting at wavelengths of about 3-50 m, are often designed as deep etched buried heterostructure QCLs. The buried heterostructure configuration is favored since the high thermal conductivity of the burying layers, usually of InP, and the low losses guarantee devices high power and high performance. However, if such QCLs are designed for and operated at short wavelengths, a severe disadvantage shows up: the high electric field necessary for such operation drives the operating current partly inside the insulating burying layer. This reduces the current injected into the active region and produces thermal losses, thus degrading performance of the QCL. The invention solves this problem by providing, within the burying layers, effectively designed current blocking or quantum barriers of, e.g. AIAs, InAIAs, InGaAs, InGaAsP, or InGaSb, sandwiched between the usual InP or other burying layers, intrinsic or Fe-doped. These quantum barriers reduce the described negative effect greatly and controllably, resulting in a QCL operating effectively also at short wavelengths and/or in high electric fields.

A surface emitting laser includes a conductive substrate, a metal bonding layer, a laser structure layer, an epitaxial semiconductor reflection layer, and an electrode layer. The laser structure layer has an epitaxial current-blocking layer having a current opening. Currents are transmitting through the current opening. The epitaxial current-blocking layer is grown by a semiconductor epitaxy process to confine the range of the currents to form electric fields.

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.

A semiconductor light-emitting element includes a laminated structure which has an active layer between a first conductivity-type semiconductor layer and a second conductivity-type semiconductor layer, a first semiconductor layer which includes at least the first conductivity-type semiconductor layer of the laminated structure, an insulation film which is formed on the first semiconductor layer and has an opening, and a second semiconductor layer which is formed on the insulation film and includes at least the second conductivity-type semiconductor layer of the laminated structure. The second semiconductor layer includes a first region facing the opening of the insulation film and a second region not facing the opening, and the second region has a portion with a higher impurity concentration than the first region.

A semiconductor light-emitting element includes a laminated structure which has an active layer between a first conductivity-type semiconductor layer and a second conductivity-type semiconductor layer, a first semiconductor layer which includes at least the first conductivity-type semiconductor layer of the laminated structure, an insulation film which is formed on the first semiconductor layer and has an opening, and a second semiconductor layer which is formed on the insulation film and includes at least the second conductivity-type semiconductor layer of the laminated structure. The second semiconductor layer includes a first region facing the opening of the insulation film and a second region not facing the opening, and the second region has a portion with a higher impurity concentration than the first region.

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 surface emitting laser includes a conductive substrate, a metal bonding layer, a laser structure layer, an epitaxial semiconductor reflection layer, and an electrode layer. The laser structure layer has an epitaxial current-blocking layer having a current opening. Currents are only transmitting through the current opening. The epitaxial current-blocking layer is grown by a semiconductor epitaxy process to confine the range of the currents to form electric fields.

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.