A new GaN single crystal is provided. A GaN single crystal according to the present embodiment comprises a gallium polar surface which is a main surface on one side and a nitrogen polar surface which is a main surface on the opposite side, wherein on the gallium polar surface is found at least one square area, an outer periphery of which is constituted by four sides each with a length of 2 mm or more, and, when the at least one square are is divided into a plurality of sub-areas each of which is a square of 100 μm×100 μm, pit-free areas account for 80% or more of the sub-areas.

A base substrate includes a supporting substrate and a base crystal layer provided on a main face of the supporting substrate composed of a crystal of a group 13 nitride and having a crystal growth surface. The base crystal layer includes a raised part. A reaction product of a material of the supporting substrate and the crystal of the group 13 nitride, metal of a group 13 element and/or void is present between the raised part and supporting substrate.

A base substrate includes a supporting substrate and a base crystal layer provided on a main face of the supporting substrate composed of a crystal of a group 13 nitride and having a crystal growth surface. The base crystal layer includes a raised part. A reaction product of a material of the supporting substrate and the crystal of the group 13 nitride, metal of a group 13 element and/or void is present between the raised part and supporting substrate.

The disclosure describes multilayer hard magnetic materials including at least one layer including α″-Fe.sub.16N.sub.2 and at least one layer including α″-Fe.sub.16(N.sub.xZ.sub.1-x).sub.2 or a mixture of α″-Fe.sub.16N.sub.2 and α″-Fe.sub.16Z.sub.2, where Z includes at least one of C, B, or O, and x is a number greater than zero and less than one. The disclosure also describes techniques for forming multilayer hard magnetic materials including at least one layer including α″-Fe.sub.16N.sub.2 and at least one layer including α″-Fe.sub.16(N.sub.xZ.sub.1-x).sub.2 or a mixture of α″-Fe.sub.16N.sub.2 and α″-Fe.sub.16Z.sub.2 using chemical vapor deposition or liquid phase epitaxy.

A light-emitting device includes: a substrate; and a laminated structure provided at the substrate and having a plurality of columnar parts. The columnar part has: an n-type first semiconductor layer; a p-type second semiconductor layer; a light-emitting layer provided between the first semiconductor layer and the second semiconductor layer; and an electrode provided on a side opposite to a side of the substrate, of the laminated structure. The first semiconductor layer is provided between the light-emitting layer and the substrate. An end part on a side opposite to a side of the substrate, of the light-emitting layer, has a first facet surface. An end part on a side opposite to a side of the substrate, of the second semiconductor layer, has a second facet surface. A relation of θ2≤θ1 is satisfied, where θ1 is a taper angle of the first facet surface, and θ2 is a taper angle of the second facet surface. θ1 is 70° or smaller, and θ2 is 30° or greater.

An alumina substrate having a carbon-containing phase with an AlN layer formed on a surface of the alumina substrate.

An alumina substrate having a carbon-containing phase with an AlN layer formed on a surface of the alumina substrate.

A surface-coated cutting tool has a hard coating layer and a tool body, which is coated with a lower layer including a TiCN layer having at least an NaCl type face-centered cubic crystal structure and an upper layer formed of a TiAlCN layer having a single phase crystal structure of NaCl type face-centered cubic crystals or a mixed phase crystal structure of NaCl type face-centered cubic crystals and hexagonal crystals. The tool body is further coated with an outermost surface layer including an Al.sub.2O.sub.3 layer, when the layer of a complex nitride or complex carbonitride of Ti and Al is expressed by the composition formula: (Ti.sub.1-xAl.sub.x)(C.sub.yN.sub.1-y), the average amount Xave of Al in Ti and Al and the average amount Yave of C in C and N (both Xave and Yave are atomic ratios) respectively satisfy 0.60≦Xave≦0.95 and 0≦Yave≦0.005.

A surface-coated cutting tool has a hard coating layer and a tool body, which is coated with a lower layer including a TiCN layer having at least an NaCl type face-centered cubic crystal structure and an upper layer formed of a TiAlCN layer having a single phase crystal structure of NaCl type face-centered cubic crystals or a mixed phase crystal structure of NaCl type face-centered cubic crystals and hexagonal crystals. The tool body is further coated with an outermost surface layer including an Al.sub.2O.sub.3 layer, when the layer of a complex nitride or complex carbonitride of Ti and Al is expressed by the composition formula: (Ti.sub.1-xAl.sub.x)(C.sub.yN.sub.1-y), the average amount Xave of Al in Ti and Al and the average amount Yave of C in C and N (both Xave and Yave are atomic ratios) respectively satisfy 0.60≦Xave≦0.95 and 0≦Yave≦0.005.

The present invention relates to a method for producing a group III compound substrate, including: a base substrate forming step for forming a group III nitride base substrate by a vapor phase synthesis method; a seed substrate forming step for forming a seed substrate on the base substrate; and a group III compound crystal forming step for forming a group III compound crystal on the seed substrate by a hydride vapor phase epitaxy method. The group III compound substrate of the present invention is produced by the method for producing a group III compound substrate of the present invention. According to the present invention, a large-sized and high-quality group III compound substrate can be obtained at a low cost while taking advantage of the high film formation rate characteristic of the hydride vapor phase epitaxy method.