To provide a high-quality group III nitride semiconductor. A group III nitride semiconductor including an n-GaN layer composed of Al.sub.xGa.sub.1-xN (0x<1), an InGaN layer disposed on the n-GaN layer and composed of InGaN, an n-AlGaN layer disposed on the InGaN layer and composed of n-type Al.sub.yGa.sub.1-yN (0y<1), and a functional layer disposed on the n-AlGaN layer, wherein the concentration of Mg in the n-GaN layer is higher than the concentration of Mg in the n-AlGaN layer.

Provided is a semiconductor laser diode. Although the materials used in the conventional technology can reduce the strain, the selections of materials are relatively limited and the carrier confinement ability is not good. To solve the above-mentioned problems, a phosphorus-containing semiconductor layer is provided in a laser diode. As such, it can effectively reduce the strain of the active region or the total strain of the laser diode, and improve the carrier confinement capability of the active region. Therefore, it can effectively reduce the total strain or significantly improve carrier confinement under appropriate conditions of the laser diode. In some cases, it has the aforesaid effects. The phosphorus-containing semiconductor layer is suitable for an active region with one or more active layers. Especially after the phosphorus-containing semiconductor layer is provided in the active region with multiple active layers, high temperature performance are significantly improved or enhanced.

A photonic integrated circuit device includes a passive waveguide section formed over a substrate, a quantum cascade laser (QCL) gain section formed over the substrate and adjacent to the passive waveguide section, and a taper section disposed between and in contact with each of the passive waveguide section and the QCL gain section. In some embodiments, the passive waveguide section includes a passive waveguide core layer disposed between a first cladding layer and a second cladding layer. In some examples, the QCL gain section includes a QCL active region disposed between a first confinement layer and a second confinement layer, where the QCL active region has a lower index of refraction than each of the first and second confinement layers. In some embodiments, the taper section is configured to optically couple the QCL gain section to the passive waveguide section.

A light-emitting device may comprise a set of layers comprising a substrate layer, and a set of epitaxial layers deposited on the substrate layer. The set of epitaxial layers may include a strained layer. The strained layer may include a set of active zones to be used to generate optical gain. The light-emitting device may comprise a set of trenches etched into a subset of the set of layers of the light-emitting device. The set of trenches may prevent a set of defects or dislocations in a wafer from which the light-emitting device was formed from propagating into the set of active zones.

A semiconductor laser includes an active layer which is provided between the p-type semiconductor region and the n-type semiconductor region and has a type II quantum well structure. The type II quantum well structure includes a well layer made of a III-V compound semiconductor and a plurality of barrier layers. The well layer includes a first region and a second region, the first region having a low potential for electrons in the well layer and a high potential for holes in the well layer, the second region having a high potential for electrons in the well layer and a low potential for holes in the well layer. The first region and the second region of the well layer are arranged in a direction from one of the barrier layers to another of the barrier layers.

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.

To provide a high-quality group III nitride semiconductor. A group III nitride semiconductor including an n-GaN layer composed of Al.sub.xGa.sub.1xN(0x<1), an InGaN layer disposed on the n-GaN layer and composed of InGaN, an n-AlGaN layer disposed on the InGaN layer and composed of n-type Al.sub.yGa.sub.1yN (0y<1), and a functional layer disposed on the n-AlGaN layer, wherein the concentration of Mg in the n-GaN layer is higher than the concentration of Mg in the n-AlGaN layer.

A semiconductor laser element includes a first nitride semiconductor layer of a first conductivity-type; a second nitride semiconductor layer of a second conductivity-type; and an active region disposed between the first nitride semiconductor layer and the second nitride semiconductor layer. The active region includes a first barrier layer, an intermediate layer, a well layer and a second barrier layer. A lattice constant of the intermediate layer is greater than a lattice constant of each of the first barrier layer and the second barrier layer, and smaller than a lattice constant of the well layer. A thickness of the intermediate layer is greater than a thickness of the well layer. The well layer and the second barrier layer are in contact with each other, or a distance between the well layer and the second barrier layer is smaller than a distance between the first barrier layer and the well layer.

A distributed feedback (DFB) laser outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The DFB laser includes a separate confinement heterostructure layer positioned between the quantum well active layer and then-type cladding layer. The DFB laser includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and then-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The DFB laser has a function to select a specific wavelength by returning a specific wavelength in the wavelength-variable laser.

A wavelength-variable laser outputting a predetermined wavelength of laser light includes: a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction; a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer; and an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer.