Method for manufacturing nitride semiconductor substrate, nitride semiconductor substrate and layered structure

A method for manufacturing a nitride semiconductor substrate, which is a method for manufacturing a nitride semiconductor substrate with a vapor deposition method, comprising:

• a step of preparing a base substrate comprising a single crystal of a group III nitride semiconductor, and having a main surface whose closest low index plane is a (0001) plane;
• a step of forming a mask layer having a plurality of openings on the main surface of the base substrate;
• a first step of epitaxially growing a single crystal of a group III nitride semiconductor on the main surface of the base substrate through the openings of the mask layer, the single crystal of the group III nitride semiconductor being sandwiched between a pair of inclined interfaces other than the (0001) plane and having a top surface with the (0001) plane exposed,
• then, forming a plurality of concaves composed of inclined interfaces other than the (0001) plane on the top surface, gradually expanding the inclined interfaces toward an upper side of the main surface of the base substrate, making the (0001) plane disappear from the top surface, and growing a first layer whose surface is composed only of the inclined interfaces;
• and
• a second step of epitaxially growing a single crystal of a group III nitride semiconductor on the first layer, making the inclined interfaces disappear, and growing a second layer having a mirror surface,
• wherein in the first step, at least one valley and a plurality of tops are formed at an upper side of each of the plurality of openings of the mask layer by forming the plurality of concaves on the top surface of the single crystal and making the (0001) plane disappear, and
• observation of an arbitrary cross section perpendicular to the main surface reveals that,
• an average distance between a pair of tops separated in a direction along the main surface is more than 100 μm, the pair of tops being closest to each other among the plurality of tops, with one valley sandwiched between them.