A group-III-nitride structure and a manufacturing method thereof are provided. In the manufacturing method, a first mask layer is first formed on a substrate; an uncoalesced second group-III-nitride epitaxial layer is formed by performing a first epitaxial growth with the first mask layer as a mask; and a second mask layer is formed at least on the second group-III-nitride epitaxial layer; a third group-III-nitride epitaxial layer is laterally grown and formed by performing a second epitaxial growth on the second group-III-nitride epitaxial layer with the second mask layer as a mask, where the second group-III-nitride epitaxial layer is coalesced by the third group-III-nitride epitaxial layer; a fourth group-III-nitride epitaxial layer is formed by performing a third epitaxial growth on the third group-III-nitride epitaxial layer.

A group-III-nitride structure and a manufacturing method thereof are provided. In the manufacturing method, a first mask layer is first formed on a substrate; an uncoalesced second group-III-nitride epitaxial layer is formed by performing a first epitaxial growth with the first mask layer as a mask; and a second mask layer is formed at least on the second group-III-nitride epitaxial layer; a third group-III-nitride epitaxial layer is laterally grown and formed by performing a second epitaxial growth on the second group-III-nitride epitaxial layer with the second mask layer as a mask, where the second group-III-nitride epitaxial layer is coalesced by the third group-III-nitride epitaxial layer; a fourth group-III-nitride epitaxial layer is formed by performing a third epitaxial growth on the third group-III-nitride epitaxial layer.

A nitride semiconductor laminate includes: a substrate comprising a group III nitride semiconductor and including a surface and a reverse surface, the surface being formed from a nitrogen-polar surface, the reverse surface being formed from a group III element-polar surface and being provided on the reverse side from the surface; a protective layer provided at least on the reverse surface side of the substrate and having higher heat resistance than the reverse surface of the substrate; and a semiconductor layer provided on the surface side of the substrate and comprising a group III nitride semiconductor. The concentration of O in the semiconductor layer is lower than 1×10.sup.17 at/cm.sup.3.

A nitride semiconductor laminate includes: a substrate comprising a group III nitride semiconductor and including a surface and a reverse surface, the surface being formed from a nitrogen-polar surface, the reverse surface being formed from a group III element-polar surface and being provided on the reverse side from the surface; a protective layer provided at least on the reverse surface side of the substrate and having higher heat resistance than the reverse surface of the substrate; and a semiconductor layer provided on the surface side of the substrate and comprising a group III nitride semiconductor. The concentration of O in the semiconductor layer is lower than 1×10.sup.17 at/cm.sup.3.

A buffer layer on a silicon carbide substrate and a method of forming the same are disclosed. The buffer layer includes at least two layers of silicon carbide films, in which at least each lower one is doped at a top surface thereof with predetermined ions. As a result, at the top surface of the silicon carbide film, a barrier with different parameter is formed, which can block dislocation defects that have spread into the silicon carbide film from further upward propagation in the silicon carbide film.

A free-standing substrate, for growing epitaxial crystal composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof, includes a nitrogen polar surface and group 13 element polar surface. The nitrogen polar surface is warped in a convex shape, and a chamfer part is provided in an outer peripheral part of the nitrogen polar surface.

The substrate is doped with P, has a resistivity adjusted to 1.05 mΩ.Math.cm or less, and includes defects, formed in the crystal by the aggregation of P, which are Si—P crystal defects substantially. The method includes a step of forming a silicon oxide film on the backside of the substrate with a thickness of 300 nm or more and 700 nm or less, a step of mirror-polishing the substrate, and after the mirror-polishing step, a heat treatment step of the substrate mounted on a substrate holder made of Si or SiC, on the holder surface a silicon oxide film is formed with the thickness between 200 nm and 500 nm, wherein the thickness X of the silicon oxide film of the holder and the thickness Y of that on the backside of the substrate satisfy a relational expression Y=C−X, where C is a constant between 800 and 1000.

A rare earth-containing SiC substrate includes a rare earth element and Al. A concentration of the rare earth element is from 1×10.sup.16 atoms/cm.sup.3 to 1×10.sup.19 atoms/cm.sup.3 inclusive and a concentration of Al is from 1×10.sup.16 atoms/cm.sup.3 to 1×10.sup.21 atoms/cm.sup.3 inclusive.

According to one embodiment, a wafer includes a substrate and a crystal layer. The substrate includes a plurality of SiC regions including SiC and an inter-SiC region including Si provided between the SiC regions. The crystal layer includes a first layer, and a first intermediate layer provided between the substrate and the first layer in a first direction. The first layer includes SiC and nitrogen. The first intermediate layer includes SiC and nitrogen. A second concentration of nitrogen in the first intermediate layer is higher than a first concentration of nitrogen in the first layer.

An object is to provide a nonpolar or semipolar GaN substrate having improved size and crystal quality. A self-standing GaN substrate has an angle between the normal of the principal surface and an m-axis of 0 degrees or more and 20 degrees or less, wherein: the size of the projected image in a c-axis direction when the principal surface is vertically projected on an M-plane is 10 mm or more; and when an a-axis length is measured on an intersection line between the principal surface and an A-plane, a low distortion section with a section length of 6 mm or more and with an a-axis length variation within the section of 10.0×10.sup.−5 Å or less is observed.