Patent ID: 8039130

Claim:
A layered structure comprising: a substrate including a base layer and an AlN underlying layer of a first group-III nitride epitaxially formed on said base layer; and a crystal layer made of a second group-III nitride, wherein an inplane lattice constant of said AlN is less than an inplane lattice constant of said second group-III nitride; wherein, before a heating process that is different from an epitaxial forming process, a surface of said underlying layer has a geometry defined by surface irregularities comprising a plurality of fine pits distributed within a substantially flat surface; wherein, after the heating process that is different from an epitaxial forming process, a textured geometry is provided on an entire surface of said underlying layer, said textured geometry being defined by surface irregularities comprising a plurality of crystalline island projections, so that a frequency of said surface irregularities of said irregular geometry of said textured geometry after said heating process is larger than a frequency of said surface irregularities of said geometry of said underlying layer before said heating process, and so that a surface roughness of said underlying layer is 1 to 5 nm; wherein voids defined by said textured geometry of said underlying layer exist discretely at an interface between said crystal layer and said underlying layer; and wherein said crystal layer is adjacent only to said underlying layer and said voids.