There is provided a semiconductor substrate including: a sapphire substrate; an intermediate layer formed of gallium nitride with random crystal directions and provided on the sapphire substrate; and at least one or more semiconductor layers each of which is formed of a gallium nitride single crystal and that are provided on the intermediate layer.

In the present invention, in producing a SiC single crystal in accordance with a solution method, a crucible containing SiC as a main component and having an oxygen content of 100 ppm or less is used as the crucible to be used as a container for a Si—C solution. In another embodiment, a sintered body containing SiC as a main component and having an oxygen content of 100 ppm or less is placed in the crucible to be used as a container for a Si—C solution. The SiC crucible and SiC sintered body are obtained by molding and baking a SiC raw-material powder having an oxygen content of 2000 ppm or less. SiC, which is the main component of these, serves as a source for Si and C and allows Si and C to elute into the Si—C solution by heating.

In the present invention, in producing a SiC single crystal in accordance with a solution method, a crucible containing SiC as a main component and having an oxygen content of 100 ppm or less is used as the crucible to be used as a container for a Si—C solution. In another embodiment, a sintered body containing SiC as a main component and having an oxygen content of 100 ppm or less is placed in the crucible to be used as a container for a Si—C solution. The SiC crucible and SiC sintered body are obtained by molding and baking a SiC raw-material powder having an oxygen content of 2000 ppm or less. SiC, which is the main component of these, serves as a source for Si and C and allows Si and C to elute into the Si—C solution by heating.

A base substrate includes a supporting substrate comprising aluminum oxide, and a base crystal layer provided on a main face of the supporting substrate, comprising a crystal of a nitride of a group 13 element and having a crystal growth surface. At lease one of a metal of a group 13 element and a reaction product of a material of the supporting substrate and the crystal of the nitride of the group 13 element is present between the raised part and the supporting substrate. The reaction product contains at least aluminum and a group 13 element.

A group 13 nitride crystal layer is composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof, and the group 13 nitride crystal layer includes an upper surface and bottom surface. The group 13 nitride crystal layer includes high-luminance layers and low-luminance layers being present alternately, and the low-luminance layers have thicknesses of 3 or larger and 10 or smaller provided that 1 is assigned to a thickness of the high-luminance layer, when a cross section of the group 13 nitride crystal layer cut in a direction perpendicular to the upper surface is observed by cathode luminescence.

A group 13 nitride crystal layer is composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof, and the group 13 nitride crystal layer includes an upper surface and bottom surface. The group 13 nitride crystal layer includes high-luminance layers and low-luminance layers being present alternately, and the low-luminance layers have thicknesses of 3 or larger and 10 or smaller provided that 1 is assigned to a thickness of the high-luminance layer, when a cross section of the group 13 nitride crystal layer cut in a direction perpendicular to the upper surface is observed by cathode luminescence.

An object of the present invention is to provide a method for producing a group III nitride crystal in which generation of breaking or cracks is less likely to occur. To achieve the object, the method for producing a group III nitride crystal includes: seed crystal preparation including disposing a plurality of crystals of a group III nitride as a plurality of seed crystals on a substrate; and crystal growth including growing group III nitride crystals by contacting a surface of each of the seed crystals with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen. In the seed crystal preparation, the plurality of seed crystals are disposed within a hexagonal region provided on the substrate.

An object of the present invention is to provide a method for producing a group III nitride crystal in which generation of breaking or cracks is less likely to occur. To achieve the object, the method for producing a group III nitride crystal includes: seed crystal preparation including disposing a plurality of crystals of a group III nitride as a plurality of seed crystals on a substrate; and crystal growth including growing group III nitride crystals by contacting a surface of each of the seed crystals with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen. In the seed crystal preparation, the plurality of seed crystals are disposed within a hexagonal region provided on the substrate.

A method for producing a Group III nitride semiconductor includes feeding a nitrogen-containing gas into a molten mixture of a Group III metal and a flux placed in a furnace, to thereby grow a Group III nitride semiconductor on a seed substrate. At least an oxidation amount of Na, serving as the flux, is controlled outside the furnace, and the controlled Na is fed into the furnace.

A method for producing a Group III nitride semiconductor includes feeding a nitrogen-containing gas into a molten mixture of a Group III metal and a flux placed in a furnace, to thereby grow a Group III nitride semiconductor on a seed substrate. At least an oxidation amount of Na, serving as the flux, is controlled outside the furnace, and the controlled Na is fed into the furnace.