In at least one embodiment, a semiconductor laser is constructed to have a waveguide core including an active region, a top cladding, and a bottom cladding. The top cladding is positioned above the waveguide core and comprises a dielectric layer and a metal layer and optionally a thin semiconductor contact layer. In at least one embodiment of the semiconductor laser, the top cladding is absent a semiconductor material which is able to contain at least 1% of an optical wave that is generated within the waveguide core.

A nitride semiconductor device includes a GaN substrate in which an angle between a principal surface and an m-plane of GaN is 5 or more and +5 or less, a first intermediate layer disposed on the principal surface of the substrate and made of Al.sub.zGa.sub.(1-z)N (0z1), and a second intermediate layer disposed on a principal surface of the first intermediate layer, having an Al content different from that of the first intermediate layer, and made of Al.sub.x1In.sub.y1Ga.sub.(1-x1-y1) (0x11, 0y11). A quantum cascade laser includes the nitride semiconductor device.

A semiconductor device and the like having high quantum efficiency or high sensitivity in a near-infrared to infrared region is provided. The semiconductor device includes: a substrate; a multiple quantum well structure disposed on the substrate, and including a plurality of pairs of a layer a and a layer b; and a crystal-adjusting layer disposed between the substrate and the multiple quantum well structure. The crystal-adjusting layer includes a first adjusting layer which is made of the same material as the substrate and is in contact with the substrate, and a second adjusting layer which is made of the same material as the layer a or the layer b of the multiple quantum well structure and is in contact with the multiple quantum well structure.

An interband cascade (IC) light emitting device comprising a plurality of interband cascade stages, wherein at least one of the IC stages is constructed to have an electron injector made of one or more QWs, a type-I quantum well (QW) active region, a barrier layer positioned between the active region and the electron injector, a hole injector made of one or more QWs, and a barrier layer positioned between the active region and the hole injector. In at least one embodiment, a type II heterointerface layer is between the electron injector and an adjacent hole injector. The well layer of the type-I QW active region has compressive strain, while the barrier layers which flank the type-I QW active region comprise tensile strain layers. In certain embodiments, the electron injector and the hole injector comprise tensile strained layers.

Semiconductor laser architectures that provide weak index guiding of interband cascade lasers (ICLs) processed on a native III-V substrate and of ICLs grown on silicon or integrated on silicon by heterogeneous bonding. Weak index guiding of a ridge waveguide semiconductor laser can enhance the stability of lasing in the fundamental lateral mode, so as to allow a wider ridge to maintain stable single-lateral-mode operation.