An n-side composition gradient layer includes an intermediate layer and composition continuous gradient layers. The intermediate layer is the group III nitride semiconductor layer containing In. The composition continuous gradient layers are group III nitride semiconductor layers in which an In composition changes in a direction perpendicular to a boundary surface between a well layer and a barrier layer. A thickness of the intermediate layer is thinner than a thickness of the well layer. An In composition of the intermediate layer is equal to or less than an In composition of the well layer. In the composition continuous gradient layers, the In composition continuously changes in a streamline manner toward the intermediate layer.

A semiconductor laser element includes: an n-side semiconductor layer formed of a nitride semiconductor; an active layer disposed on or above the n-side semiconductor layer and formed of a nitride semiconductor; a p-side semiconductor layer disposed on the active layer, formed of a nitride semiconductor, and including: an undoped first part disposed in contact with an upper face of the active layer and comprising at least one semiconductor layer, an electron barrier layer disposed in contact with an upper face of the first part, containing a p-type impurity, and having a band gap energy that is larger than a band gap energy of the first part, and a second part disposed in contact with the upper face of the electron barrier layer and comprising at least one p-type semiconductor layer containing a p-type impurity; and a p-electrode disposed in contact with the upper face of the second part.

A quantum cascade laser of an embodiment includes a semiconductor stacked body in which a ridge waveguide is provided. The semiconductor stacked body includes an active layer including a quantum well region including a layer including Al; and the active layer emits laser light. The layer that includes Al includes first regions, and a second region interposed between the first regions; the first region includes Al oxide and reaches a prescribed depth inward from an outer edge of the active layer along a direction parallel to a surface of the active layer in a cross section orthogonal to the optical axis; and the second region does not include Al oxide.

The diode laser comprises a laser bar having a semiconductor body and an active layer, wherein the laser bar has a plurality of individual emitters. At least some individual emitters are respectively assigned a section of the semiconductor body and a current regulating element's connected in series therewith, such that, during operation of the individual emitters as intended, an electrical operating current I.sub.0 fed to the individual emitter in each case flows completely through the assigned section of the semiconductor body and in the process a voltage drop U.sub.H occurs at the section and at least part of said operating current I.sub.0 flows through the assigned current regulating element and experiences an electrical resistance R.sub.S in the process. In the case of the individual emitters, the current regulating element assigned in each case is configured such that the resistance Rg at an operating temperature T.sub.0 has a positive temperature coefficient dR.sub.S/dT|.sub.T0. Alternatively or additionally, the resistance R.sub.S is greater than IΔU.sub.H/I.sub.0, wherein ΔU.sub.H is the change in the voltage drop U.sub.H at the assigned section of the semiconductor body in the event of an increase in the temperature T of the individual emitter from an operating temperature T.sub.0 by 1 K.

A vertical cavity surface emitting device includes a substrate, a first multilayer film reflecting mirror on the substrate, a first semiconductor layer on the first multilayer film reflecting mirror, a light-emitting layer on the first semiconductor layer, and a second semiconductor layer on the light-emitting layer. The second semiconductor layer includes a low resistance region and a high resistance region on an upper surface. The high resistance region is depressed from the low resistance region toward the light-emitting layer outside the low resistance region and impurities of the second conductivity type are inactivated in the high resistance region such that the high resistance region has an electrical resistance higher than an electrical resistance of the low resistance region. A light-transmitting electrode layer is in contact with the low resistance region and the high resistance region, and a second multilayer film reflecting mirror is on the light-transmitting electrode layer.

A semiconductor device comprising: a layered structure 20 configured by layering a first compound semiconductor layer 21, an active layer 23, and a second compound semiconductor layer 22; a substrate 11; a first light reflecting layer 41 arranged on the first surface side of the first compound semiconductor layer 21; and a second light reflecting layer 42 arranged on the second surface side of the second compound semiconductor layer 22, wherein the second light reflecting layer 42 has a flat shape; a concave surface portion 12 is formed on a substrate surface 11b; the first light reflecting layer 41 is formed on at least the concave surface portion 12; the first compound semiconductor layer 21 is formed to extend from the substrate surface 11b onto the concave surface portion 12; and a cavity is present between the first light reflecting layer 41 formed on the concave surface portion 12 and the first compound semiconductor layer 21.

A laser module including a quantum cascade laser that includes a substrate having a main surface, a first clad layer provided on the main surface, an active layer provided on the first clad layer, and a second clad layer provided on the active layer, and a lens that has a lens plane disposed at a position facing the end surface of the active layer. An end surface of the active layer constitutes a resonator that causes light of a first frequency and light of a second frequency to oscillate, and the active layer is configured to generate a terahertz wave of a differential frequency between the first frequency and the second frequency. The substrate is in direct contact or indirect contact with the lens plane, and the end surface of the active layer is inclined with respect to a portion facing the end surface in the lens plane.

A compound semiconductor layer stack includes: a first layer 11 being formed on a base 14 and including an island-shaped Al.sub.x1In.sub.y1Ga.sub.(1-x1-y1)N; a second layer 12 being formed on the first layer 11 and including Al.sub.x2In.sub.y2Ga.sub.(1-x2-y2)N; and a third layer 13 being formed on an entire surface including a top of the second layer 12, the third layer 13 including Al.sub.x3Ga.sub.(1-x3)N (provided that the following hold true: 0≤x1<1; 0≤x2<1; 0≤x3<1; 0≤y1<1; and 0<y2<1), and the third layer 13 has a top surface 13A that is flat.

The laser device includes a first mirror and a second mirror forming a resonator, a gain medium disposed between the first mirror and the second mirror and having a light emitting surface, an antireflection film provided on the light emitting surface of the gain medium, at least one optical element disposed between the gain medium and the second mirror, and a diffraction grating disposed between the optical element and the second mirror. The gain medium is a semiconductor layered body including an active layer and having a varying gain distribution in at least a first direction within the light emitting surface, and includes no waveguide.

An optical device has a gallium and nitrogen containing substrate including a surface region and a strain control region, the strain control region being configured to maintain a quantum well region within a predetermined strain state. The device also has a plurality of quantum well regions overlying the strain control region.