Quasi-strain-free GaN on van der Waals substrates: the case of graphene and muscovite mica

The use of van der Waals substrates, in which the epitaxial growth is achieved through weak dipolar interactions, can result in a significant relaxation of the epilayer strain, facilitating at the same time layer detachment. Here, we study the case of GaN layers grown on graphene and muscovite mica. Morphology, surface potential and strain relaxation of GaN are addressed. In the case of graphene, we show it experiences interesting transformations during the growth of GaN, resulting in the intercalation of metal atoms below the graphene layer. In the case of mica, we find that part of the strain accumulated in the GaN layer relaxes by the formation of three-dimensional structures in the shape of telephone cord buckles, straight blisters or by more complex arrangements. Their characteristics are studied in relation to the initial compressive strain and the elastic parameters of the materials.