Patent ID: 7357837

Claim:
A method of making a GaN single crystal substrate comprising: a buffer layer forming step of forming a buffer layer on said GaAs substrate; a lower epitaxial layer growing step of growing on said buffer layer a lower epitaxial layer made of GaN; a mask layer forming step of forming on said lower epitaxial layer, a mask layer having a plurality of opening windows disposed separate from each other, the mask layer having a thickness in the range of 0.05 μm to 0.5 μm; and an epitaxial layer growing step of growing on said mask layer an upper epitaxial layer made of GaN, wherein said mask forming step includes arranging said plurality of said opening windows with a pitch L in a <10-10> direction of said lower epitaxial layer so as to form a <10-10> window group, and arranging a plurality of <10-10> window groups in parallel with a pitch d (0.75L≦d≦1.3L) in a <1-210> direction of said lower epitaxial layer, wherein said upper expitaxial layer growing step includes initially growing a hexagonal pyramid shaped crystal in each of said opening windows whereafter each crystal connects with other crystals on said mask layer without interstices therebetween, and wherein said opening windows of said mask layer are rectangular windows in an oblong form having a longitudinal direction aligning with a <10-10> direction of said lower epitaxial layer, a plurality of said rectangular windows being arranged with a pitch L in said <10-10> direction so as to form a <10-10> rectangular window group, a plurality of <10-10> rectangular window groups being arranged in parallel with a pitch d in a <1-210> direction of said lower epitaxial layer.