A semiconductor device comprises a substrate, one or more first III-semiconductor layers, and a plurality of superlattice structures between the substrate and the one or more first layers. The plurality of superlattice structures comprises an initial superlattice structure and one or more further superlattice structures between the initial superlattice structure and the one or more first layers. The plurality of superlattice structures is configured such that a strain-thickness product of semiconductor layer pairs in each superlattice structure of the one or more further superlattice structures is greater than or equal to a strain-thickness product of semiconductor layer pairs in superlattice structure(s) of the plurality of superlattice structures between that superlattice structure and the substrate. The plurality of superlattice structures is also configured such that a strain-thickness product of semiconductor layer pairs in at least one of the one or more further superlattice structures is greater than a strain-thickness product of semiconductor layer pairs in the initial superlattice structure.

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 structure can include a substrate comprising a first in-plane lattice constant, a graded layer on the substrate, and a first region of the graded layer comprising a first epitaxial oxide material comprising a second in-plane lattice constant. The graded layer on the substrate can include (Al.sub.x1Ga.sub.1−x1).sub.y1O.sub.z1, wherein x1 is from 0 to 1, wherein y1 is from 1 to 3, wherein z1 is from 2 to 4, and wherein x1 varies in a growth direction such that the graded layer has the first in-plane lattice constant adjacent to the substrate and a second in-plane lattice constant at a surface of the graded layer opposite the substrate. In some cases, a semiconductor structure includes a first region comprising a first epitaxial oxide material; a second region comprising a second epitaxial oxide material; and the graded region located between the first and the second regions.

A semiconductor laser element includes a ridge, and includes: a p-type first clad layer; and a p-type second clad layer arranged on the p-type first clad layer, the p-type first clad layer has a superlattice structure of an Al.sub.xGa.sub.1-xN layer and an Al.sub.yGa.sub.1-yN layer (0≤x≤y≤1), the p-type second clad layer includes Al.sub.zGa.sub.1-zN (0≤z≤y), the p-type first clad layer includes: a flat portion on which the p-type second clad layer is not arranged; and a protruding portion which protrudes upward from the flat portion and on which the p-type second clad layer is arranged, and the height of the protruding portion protruding from the flat portion is less than the thickness of the p-type first clad layer in the flat portion.

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.

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 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 layer structure may include a substrate, a blocking layer disposed over the substrate, and one or more epitaxial layers disposed over the blocking layer. The blocking layer may have a thickness of between 50 nanometers (nm) and 4000 nm. The blocking layer may be configured to suppress defects from the substrate propagating to the one or more epitaxial layers. The one or more epitaxial layers may include a quantum-well layer that includes a quantum-well intermixing region formed using a high temperature treatment.

A semiconductor layer structure may include a substrate, a blocking layer disposed over the substrate, and one or more epitaxial layers disposed over the blocking layer. The blocking layer may have a thickness of between 50 nanometers (nm) and 4000 nm. The blocking layer may be configured to suppress defects from the substrate propagating to the one or more epitaxial layers. The one or more epitaxial layers may include a quantum-well layer that includes a quantum-well intermixing region formed using a high temperature treatment.

An embodiment relates to a surface emitting laser device and a light emitting device including the same. A surface emitting laser device according to the embodiment may include a first reflective layer; an active layer disposed on the first reflective layer; an aperture area disposed on the active layer and including an aperture and an insulating region; and a second reflective layer disposed in the aperture area. The active layer may comprise a plurality of quantum wells, quantum barriers, and intermediate layers disposed between the quantum wells and the quantum barriers. The quantum wells and the quantum barriers may include a ternary material, and the intermediate layers may comprise a binary material.