A light emitting apparatus includes a laminated structure including a plurality of columnar section assemblies each formed of p columnar sections. The p columnar sections each include a light emitting layer. When viewed in the lamination direction of the laminated structure, the ratio of the maximum width to the minimum width of the light emitting layer in each of q first columnar sections out of the p columnar sections is greater than the ratio of the light emitting layer in each of r second columnar sections out of the p columnar sections. The light emitting layer in each of the p columnar sections does not have a rotationally symmetrical shape. The parameter p is an integer greater than or equal to 2. The parameter q is an integer greater than or equal to 1 but smaller than p. The parameter r is an integer that satisfies r=pq.

A p-type semiconductor layer includes a plurality of unit semiconductor layers, and each of the plurality of unit semiconductor layers includes a p-type nitride semiconductor whose main surface is a polar surface or a semi-polar surface. The nitride semiconductor constituting the unit semiconductor layer includes nitrogen and two or more elements, and each of the plurality of unit semiconductor layers has a composition changing in a stacking direction such that, for example, a lattice constant in a c-axis direction increases in a c-axis positive direction.

A semiconductor light-emitting device including a P-type semiconductor cladding layer, an N-type semiconductor layer, a light-emitting layer, and a hole injection layer is provided. The P-type semiconductor cladding layer is doped with magnesium. The light-emitting layer is disposed between the P-type semiconductor cladding layer and the N-type semiconductor layer. The hole injection layer is disposed between the P-type semiconductor cladding layer and the light-emitting layer. The hole injection layer includes a first super lattice structure formed by alternately stacking a plurality of magnesium nitride layers and a plurality of semiconductor material layers. The chemical formula of each of the semiconductor material layers is Al.sub.xIn.sub.yGa.sub.1-x-yN, and 0x1, 0y1, and 0x+y1.

In some embodiments, a semiconductor structure includes: a first epitaxial oxide semiconductor layer; a metal layer; and a contact layer adjacent to the metal layer, and between the first epitaxial oxide semiconductor layer and the metal layer. The contact layer can include an epitaxial oxide semiconductor material. The contact layer can also include a region comprising a gradient in a composition of the epitaxial oxide semiconductor material adjacent to the metal layer, or a gradient in a strain of the epitaxial oxide semiconductor material over a region adjacent to the metal layer.

A semiconductor light-emitting device including a P-type semiconductor cladding layer, an N-type semiconductor layer, a light-emitting layer, and a hole injection layer is provided. The P-type semiconductor cladding layer is doped with magnesium. The light-emitting layer is disposed between the P-type semiconductor cladding layer and the N-type semiconductor layer. The hole injection layer is disposed between the P-type semiconductor cladding layer and the light-emitting layer. The hole injection layer includes a first super lattice structure formed by alternately stacking a plurality of magnesium nitride layers and a plurality of semiconductor material layers. The chemical formula of each of the semiconductor material layers is Al.sub.xIn.sub.yGa.sub.1-x-yN, and 0x1, 0y1, and 0x+y1.

In some embodiments, a semiconductor structure includes: a first epitaxial oxide semiconductor layer; a metal layer; and a contact layer adjacent to the metal layer, and between the first epitaxial oxide semiconductor layer and the metal layer. The contact layer can include an epitaxial oxide semiconductor material. The contact layer can also include a region comprising a gradient in a composition of the epitaxial oxide semiconductor material adjacent to the metal layer, or a gradient in a strain of the epitaxial oxide semiconductor material over a region adjacent to the metal layer.

A method of growing III-nitride-based devices, such as light emitting diodes (LEDs) and laser diodes (LDs) on or above a strain relaxed template (SRT). The SRT uses a thin, thermally decomposed, InGaN underlayer, which is referred to as a decomposition layer (DL). Above the DL is a n-type GaN or low composition InGaN decomposition stop layer (DSL). A buffer layer comprising an n-type InGaN/GaN superlattice (SL) is then grown. For an LD structure. an n-type waveguide layer comprising a second n-type InGaN/GaN SL is then grown. followed by an active region, a p-type electron blocking layer (EBL), a p-type waveguide layer comprising a p-type InGaN/GaN SL, and p-type GaN or p-type InGaN layers. For an LED structure, the waveguide layers may be omitted. In this disclosure, AlGaN means Al.sub.xGa.sub.(1-x)N with 1x0 and InGaN means In.sub.xGa.sub.(1-x)N with 1x0.

In some embodiments, a semiconductor structure includes a single crystal substrate, a first epitaxial oxide layer on the single crystal substrate, and a second epitaxial oxide layer on the single crystal substrate. The first epitaxial oxide layer can include a first oxide material with a cubic crystal symmetry. The second epitaxial oxide layer can include a second oxide material with a monoclinic crystal symmetry. The second epitaxial oxide layer can be elastically strained to the first epitaxial oxide layer. The substrate can include MgO, MgAl.sub.2O.sub.4, or -Ga.sub.2O.sub.3. The first epitaxial oxide layer can include MgO with a cubic crystal symmetry oriented in the (100) direction, and the second epitaxial oxide layer can include -Ga.sub.2O.sub.3 oriented in the (100) direction, where there is a 45 rotation around the (100) direction between the MgO and the -Ga.sub.2O.sub.3 crystal structures.

In order to provide a THz-QCL element which takes advantage of the characteristics of a ZnO-based semiconductor material, a quantum cascade laser element has a semiconductor superlattice structure (a QCL structure), wherein the semiconductor superlattice structure has a plurality of unit structures that are stacked repeatedly. Each unit structures comprises three well layers having a composition of ZnO or ZnMgO, and barrier layers having a composition of ZnMgO or MgO that separates each well layer from each other and have a higher ratio of MgO than the left and right wells.