Patent ID: 7932114

Claim:
A method of manufacturing a GaN substrate having a c-plane for manufacturing an epitaxialwafer by successively stacking at least two layers including an Al x Ga (1-x) N layer having an Al composition x greater than zero and not more than 0.3 and a thickness greater than zero and not more than 30 nm and a GaN layer on said c-plane, comprising the steps of: deciding a value t 1 found by the following expression 1 as the minimum thickness of said GaN substrate: (1.5×10 11 ×t 1( m ) 3 +1.2×10 11 ×t 2( m ) 3 )×{1/(1.5×10 11 ×t 1( m ))+1/(1.2×10 11 ×t 2( m ))}/{15.96× x ×(1− a 2/ a 1)}×( t 1( m ) +t 2( m ))+( t 1( m ) ×t 2( m ))/{5.32× x ×(1− a 2/ a 1)}−( r ( m ) 2 + h ( m ) 2 )/2 h ( m )=0 (expression 1) where t 1 (m) represents the thickness of said GaN substrate, r(m) represents the radius of said GaN substrate, t 2 (m) represents the thickness of said Al x Ga (1-x) N layer, x represents the Al composition in said Al x Ga (1-x) N layer, h(m) represents a warp of said epitaxialwafer, a 1 represents the lattice constant of GaN and a 2 represents the lattice constant of AlN; and cutting out said GaN substrate having a thickness of at least said minimum thickness and less than 400 μm from an ingot of GaN.