A semiconductor laser including a waveguide having a core, a confinement layer to bury the core, and a metallization layer. The core includes an active core region. The confinement layer surrounds the core and includes a first confinement layer between the core and the semiconductor substrate below the core, a second confinement layer above the core, and a third confinement layer to either or both sides of the core. The metallization layer is located above the confinement layers and include a first metallization layer and a second metallization layer. The first metallization layer is in direct contact with the second confinement layer and the third confinement layer, while the second metallization layer is disposed above the first layer. The first metallization layer is tuned to have a plasmon resonance corresponding to a higher order mode with high loss.

A quantum-cascade laser element includes: a semiconductor substrate; a semiconductor laminate formed on the semiconductor substrate to include a ridge portion configured to include an active layer having a quantum-cascade structure; an embedding layer including a first portion formed on a side surface of the ridge portion, and a second portion extending from an edge portion of the first portion on a side of the semiconductor substrate along a width direction of the semiconductor substrate; a metal layer formed on a top surface of the ridge portion, on the first portion, and on the second portion; and a dielectric layer disposed between the second portion and the metal layer. The dielectric layer is formed such that a part of the second portion is exposed from the dielectric layer. The metal layer is in contact with the second portion at the part.

A quantum cascade laser includes a first and a second mesa waveguides disposed on a substrate, a first electrode, a second electrode, and a current blocking region disposed burying the first and second mesa waveguides. The first and second mesa waveguides extend in a first direction. The first and second mesa waveguides are arranged apart from each other by a distance in a second direction intersecting with the first direction. The current blocking region has a first portion disposed between the first and second mesa waveguides and a second portion disposed on the first portion. The end of the first electrode and the end of the second electrode are facing each other in the second direction. The second portion protrudes from a reference plane which includes a surface of the end of the first electrode and extends in the first and second directions.

A semiconductor optical device includes: a lower mesa structure extending in a stripe shape and composed of some layers including an active layer; a buried layer configured to bury both sides of the lower mesa structure and made of indium phosphide; and an upper mesa structure extending in a stripe shape and composed of some layers including a bottom layer made of phosphorus-free materials, the bottom layer having a bottom surface protruding from a topmost layer of the lower mesa structure, the bottom surface being in contact with the lower mesa structure and the buried layer.

A quantum-cascade laser element includes: a semiconductor substrate; a semiconductor mesa formed on the semiconductor substrate to include an active layer having a quantum-cascade structure and to extend along a light waveguide direction; an embedding layer formed to interpose the semiconductor mesa along a width direction of the semiconductor substrate; a cladding layer formed at least on the semiconductor mesa; and a metal layer formed at least on the cladding layer. A thickness of the cladding layer is thinner in a second region located outside a first region in the width direction of the semiconductor substrate than in the first region of which at least a part overlaps the semiconductor mesa when viewed in a thickness direction of the semiconductor substrate. The metal layer extends over the first region and the second region.

A method for on-silicon integration of a III-V-based material component includes providing a first substrate having a silicon-based optical layer including a waveguide, transferring a second substrate of III-V-based material on the optical layer, and forming the III-V component from the second substrate, so as to enable a coupling between the waveguide and the III-V component, by preserving a III-V-based material layer extending laterally. The method also includes forming by epitaxy from the III-V layer, an InP:Fe-based structure laterally bordering the III-V component, forming a layer including contacts configured to contact the III-V component, and transferring a third silicon-based substrate onto the layer including the contacts.

There are included: a second semiconductor layer of a second conduction-type formed to be on and in contact with the active layer; and a third semiconductor layer of a second conduction-type formed on the second semiconductor layer, the third semiconductor layer is arranged above a formation region of the active layer, a bottom surface of the third semiconductor layer is arranged in the formation region of the active layer, and a width of the third semiconductor layer, on the active layer side, in a direction perpendicular to a waveguide direction and parallel to a plane of a substrate is set to be smaller than a width of the active layer in the same direction.

A quantum-cascade laser element includes: an embedding layer including a first portion formed on a side surface of a ridge portion, and a second portion extending from an edge portion of the first portion on a side of a semiconductor substrate along a width direction of the semiconductor substrate; and a metal layer formed at least on a top surface of the ridge portion and on the first portion. A surface of the second portion on a side opposite to the semiconductor substrate is located between a surface of an active layer on a side opposite to the semiconductor substrate and a surface of the active layer on a side of the semiconductor substrate. When viewed in the width direction of the semiconductor substrate, a part of the metal layer on the first portion overlaps the active layer. The metal layer is directly formed on the first portion.

A quantum-cascade laser element includes: a semiconductor substrate; a semiconductor mesa formed on the semiconductor substrate to include an active layer having a quantum-cascade structure and to extend along a light waveguide direction; an embedding layer formed to interpose the semiconductor mesa along a width direction of the semiconductor substrate; a cladding layer formed over the semiconductor mesa and over the embedding layer; and a metal layer formed on the cladding layer. A pair of groove portions extending along the light waveguide direction are formed in a surface on an opposite side of the cladding layer from the semiconductor substrate. The pair of groove portions are disposed in two respective outer regions when the cladding layer is equally divided into four regions in the width direction of the semiconductor substrate. The metal layer enters the pair of groove portions.

Semiconductor Quantum Cascade Lasers (QCLs), in particular mid-IR lasers emitting at wavelengths of about 3-50 μm, 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.