Patent ID: 7790489

Claim:
A method of making a III-V group nitride system semiconductor self-standing substrate, said method comprising: forming a GaN layer and a Ti thin film on an upper layer of a hetero-substrate in this order, thermally treating the substrate with the GaN layer to form a void-formed GaN layer by generating voids in the GaN layer and a hole-formed TiN layer by nitriding the Ti thin film; growing a III-V group nitride system semiconductor crystal thereon by a Hydride Vapor Phase Epitaxy (HVPE) method while generating a plurality of concaves on a crystal growth interface; flattening the crystal growth interface by growing the III-V group nitride system semiconductor crystal to fill the plurality of concaves, whereby dislocation lines generated in the crystal are gathered while reducing a dislocation density of an entire III-V group nitride system semiconductor crystal, to form a first III-V group nitride system semiconductor crystal layer that comprises a region with dislocation lines gathered densely, the dislocation lines being gathered substantially perpendicular to a surface of the substrate, and a region with dislocation lines gathered thinly; subsequently growing the crystal while keeping the crystal growth interface flattened, whereby a transitional layer is formed that the dislocation lines once gathered are uniformly dispersed again in the crystal, and a second III-V group nitride system semiconductor crystal layer is formed with a thickness of 10 μm or more on the transitional layer, the second III-V group nitride system semiconductor crystal layer having a low dislocation density and a substantially uniform dislocation density distribution; and separating the III-V group nitride system semiconductor crystal grown on the hetero-substrate from the hetero-substrate.