A nitride semiconductor laser device sequentially includes, between a nitride semiconductor substrate and an n-side cladding layer, a first nitride semiconductor layer formed of an AlGaN layer, a second nitride semiconductor layer that is formed of an AlGaN layer and has a lower Al content than the first nitride semiconductor layer, a third nitride semiconductor layer formed of a GaN layer, a fourth nitride semiconductor layer formed of an InGaN layer, and a fifth nitride semiconductor layer formed of an AlGaN layer.

Disclosed is an optically pumped vertical cavity laser structure operating in the mid-infrared region, which has demonstrated room-temperature continuous wave operation. This structure uses a periodic gain active region with type I quantum wells comprised of InGaAsSb, and barrier/cladding regions which provide strong hole confinement and substantial pump absorption. A preferred embodiment includes at least one wafer bonded GaAs-based mirror. Several preferred embodiments also include means for wavelength tuning of mid-IR VCLs as disclosed, including a MEMS-tuning element. This document also includes systems for optical spectroscopy using the VCL as disclosed, including systems for detection concentrations of industrial and environmentally important gases.

An optical semiconductor device includes an InP substrate; an active layer disposed above the InP substrate; a n-type semiconductor layer disposed below the active layer; and a p-type clad layer disposed above the active layer, wherein the p-type clad layer includes one or more p-type In.sub.1-xAl.sub.xP layers, the Al composition x of each of the one or more p-type In.sub.1-xAl.sub.xP layers is equal to or greater than a value corresponding to the doping concentration of a p-type dopant, and the absolute value of the average strain amount of the whole of the p-type clad layer is equal to or less than the absolute value of a critical strain amount obtained by Matthews' relational expression, using the entire layer thickness of the whole of the p-type clad layer as a critical layer thickness.

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.(1z)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.(1x1y1)N, 0x11, 0y11. A quantum cascade laser includes the nitride semiconductor device.

In an example, the present invention provides a method for fabricating a light emitting device configured as a Group III-nitride based laser device. The method also includes forming a gallium containing epitaxial material overlying the surface region of a substrate member. The method includes forming a p-type (Al,In,Ga)N waveguiding material overlying the gallium containing epitaxial material under a predetermined process condition. The method includes maintaining the predetermined process condition such that an environment surrounding a growth of the p-type (Al,In,Ga)N waveguide material is substantially a molecular N.sub.2 rich gas environment. The method includes maintaining a temperature ranging from 725 C to 925 C during the formation of the p-type (Al,In,Ga)N waveguide material, although there may be variations. In an example, the predetermined process condition is substantially free from molecular H.sub.2 gas.

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.

In an example, the present invention provides a method for fabricating a light emitting device configured as a Group III-nitride based laser device. The method also includes forming a gallium containing epitaxial material overlying the surface region of a substrate member. The method includes forming a p-type (Al,In,Ga)N waveguiding material overlying the gallium containing epitaxial material under a predetermined process condition. The method includes maintaining the predetermined process condition such that an environment surrounding a growth of the p-type (Al,In,Ga)N waveguide material is substantially a molecular N.sub.2 rich gas environment. The method includes maintaining a temperature ranging from 725 C to 925 C during the formation of the p-type (Al,In,Ga)N waveguide material, although there may be variations. In an example, the predetermined process condition is substantially free from molecular H.sub.2 gas.

A light-emitting device is provided. An active layer is disposed on a substrate and between the first semiconductor layer and the second semiconductor layer. The first aluminum-containing semiconductor layer is disposed between the substrate and the first semiconductor layer, and a first aluminum composition ratio of the first aluminum-containing semiconductor layer is greater than that of the first semiconductor layer. The second aluminum-containing semiconductor layer is disposed between the first aluminum-containing semiconductor layer and the first semiconductor layer, and a second aluminum composition ratio of the second aluminum-containing semiconductor layer is greater than that of the first semiconductor layer. The stack structure is disposed between the first and second aluminum-containing semiconductor layers, and the stack structure includes first, second, and third indium-containing semiconductor layers stacked in sequence. The first, second, and third indium-containing semiconductor layers are made of In.sub.a1Al.sub.b1Ga.sub.1-a1-b1N (0<a1+b1<1), In.sub.a2Al.sub.b2Ga.sub.1-a2-b2N (0<a2+b2<1, and In.sub.a3Al.sub.b3Ga.sub.1-a3-b3N (0<a3+b3<1), respectively, and 0<a3a1<a2.