Patent ID: 7713847

Claim:
A method of forming an AlGaN crystal layer, comprising the steps of: fabricating a template substrate by forming an AlN crystal layer on a specific single crystal base material, said template substrate fabrication step comprising the steps of epitaxially forming the AlN crystal layer on said single crystal base material, and then performing a step of heating said AlN crystal layer to a temperature of 1500° C. or higher, so that said AlN crystal layer, after said heating, exhibits in-plane compressive stress and has a flat surface at a substantially atomic level; and then forming an AlGaN layer on said AlN crystal layer after completing the heating step; wherein said AlGaN layer is formed at a deposition temperature higher than 1000° C. by depositing alternating layers of a first unit layer comprising a Group III nitride represented by the composition formula Al x Ga 1-x N(0≦x≦1) and a second unit layer comprising a Group III nitride represented by the composition formula Al y Ga 1-y N (0≦y≦1 and y≠x) such that the AlGaN layer has a superlattice structure.