w Al x Ga y In z N, (c2) B w Al x Ga y The growth of the layer 3b of In z N, (c3) the growth of the intermediate layer 4b of B w Al x Ga y In z N, and the layers formed in steps c1 to c3 ( At least one of 3b, 4a, 4b) is at least a three-component III-N alloy comprising aluminum and gallium, the method further comprising (d) growing the layer (3; 3 ', 3 ") of GaN do."/>