A method for manufacturing a nitride semiconductor substrate by using a vapor phase growth method, including: a step of preparing a base substrate of a single crystal of a group III nitride semiconductor and in which a low index crystal plane closest to a main surface is a (0001) plane; an etching step of the base substrate to roughen the main surface; a first step of growing a first layer by epitaxially growing a single crystal of a group III nitride semiconductor on the main surface, and at least some of the plurality of recessed portions being gradually expanded toward an upper side of the main surface of the base substrate, the first layer including a first surface from which the (0001) plane has disappeared and that is constituted only by the inclined interfaces; and a second step of growing a second layer including a mirror second surface.

A group III nitride crystal, wherein the group III nitride crystal is doped with an N-type dopant and a germanium element, the concentration of the N-type dopant is 1×10.sup.19 cm.sup.−3 or more, and the concentration of the germanium element is nine times or more higher than the concentration of the N-type dopant.

A group III nitride crystal, wherein the group III nitride crystal is doped with an N-type dopant and a germanium element, the concentration of the N-type dopant is 1×10.sup.19 cm.sup.−3 or more, and the concentration of the germanium element is nine times or more higher than the concentration of the N-type dopant.

A group III nitride crystal, wherein the group III nitride crystal is doped with an N-type dopant and a hydrogen element, and the concentration of the N-type dopant is 1×10.sup.20 cm.sup.−3 or more, and the concentration of the hydrogen element is 1×10.sup.19 cm.sup.−3 or more.

A group III nitride crystal, wherein the group III nitride crystal is doped with an N-type dopant and a hydrogen element, and the concentration of the N-type dopant is 1×10.sup.20 cm.sup.−3 or more, and the concentration of the hydrogen element is 1×10.sup.19 cm.sup.−3 or more.

A method for producing a GaN crystal that includes: (i) a seed crystal preparation step of preparing a GaN seed crystal having one or more facets selected from a {10-10} facet and a {10-1-1} facet; and (ii) a growth step of growing GaN from vapor phase on a surface comprising the one or more facets of the GaN seed crystal using GaCl.sub.3 and NH.sub.3 as raw materials.

A method for producing a GaN crystal that includes: (i) a seed crystal preparation step of preparing a GaN seed crystal having one or more facets selected from a {10-10} facet and a {10-1-1} facet; and (ii) a growth step of growing GaN from vapor phase on a surface comprising the one or more facets of the GaN seed crystal using GaCl.sub.3 and NH.sub.3 as raw materials.

It is provided a seed crystal layer, composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof, on an alumina layer on a single crystal substrate. By annealing under reducing atmosphere at a temperature of 950° C. or higher and 1200° C. or lower, convex-concave morphology is formed on a surface of the seed crystal layer so as to have an RMS value of 180 nm to 700 nm measured by an atomic force microscope. On the surface of the seed crystal layer, it is grown a group 13 nitride crystal layer composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof.

It is provided a seed crystal layer, composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof, on an alumina layer on a single crystal substrate. By annealing under reducing atmosphere at a temperature of 950° C. or higher and 1200° C. or lower, convex-concave morphology is formed on a surface of the seed crystal layer so as to have an RMS value of 180 nm to 700 nm measured by an atomic force microscope. On the surface of the seed crystal layer, it is grown a group 13 nitride crystal layer composed of a group 13 nitride crystal selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof.

A process of preparing a wafer having a diameter of two inches or more, at least a surface of the wafer being formed from a group III nitride crystal, including preparing an alkaline or acidic etching liquid containing a peroxodisulfate ion as an oxidizing agent that accepts an electron, accommodating the wafer such that the surface of the wafer is immersed in the etching liquid such that the surface of the wafer is parallel with a surface of the etching liquid; and radiating light from the surface side of the etching liquid onto the surface of the wafer without agitating the etching liquid. First and second etching areas disposed at an interval from each other are defined on the surface of the wafer. In the process of radiating the light onto the surface of the wafer, the light is radiated perpendicularly onto surfaces of the first and second etching areas.