Patent ID: 8647967

Claim:
A method of obtaining a hexagonal würtzite type epitaxial layer having a desired impurity concentration of alkali-metal, comprising: using a hexagonal würtzite substrate possessing an impurity concentration of alkali-metal that is different from the desired impurity concentration of alkali-metal of the hexagonal würtzite type epitaxial layer, determining which of a plurality of surfaces of the hexagonal würtzite substrate has a crystal plane that diffuses the alkali-metal from the hexagonal würtzite substrate into the hexagonal würtzite type epitaxial layer at a desired level, choosing a surface from the plurality of surfaces of the hexagonal würtzite substrate having a crystal plane that diffuses the alkali-metal from the hexagonal würtzite substrate into the hexagonal würtzite type epitaxial layer at the desired level, and growing the hexagonal würtzite type epitaxial layer on the chosen surface of the hexagonal würtzite substrate to obtain the desired impurity concentration of alkali-metal of the hexagonal würtzite type epitaxial layer.