Mushroom structure of GaN template for epitaxial growth of GaN

► Novel mushroom structure is formed by a simple anneal of a GaN buffer layer. ► Cap of the mushroom structure is identified as wurtzitic GaN. ► Stem region is observed to remain zinc-blende. ► Structure energy difference between the two phases drives the mushroom formation. ► This study provides a wider perspective on the use of the GaN buffer layer.