Polytypism phenomenon in GaN nanocrystals grown on van der Waals surface

Abstract

The polytypism phenomenon in the growth of nanostructures reveals new properties and opportunities for bandgap engineering by enabling controlled formation of different phases of the same material with distinct crystalline and electronic structures. In the case of III-nitrides, the occurrence of polytypism is unlikely and and has not been experimentally observed to date. Here, we report the discovery of polytypism in GaN nanocrystals (NCs) grown via the vapor-liquid-solid mechanism on the surface of a van der Waals graphene-like SiN structure. Through a detailed analysis of the diffraction patterns, we have established the formation of three structures during the growth of NCs, namely zinc-blende with the (111) plane, the 6H polytype and wurtzite with the non-polar (10-10) plane. As shown by transmission electron microscopy data, the crystal structures form within the volume of a single NC. The formation of zinc-blende and wurtzite phases is explained within the framework of classical nucleation theory, while the 6H polytype nucleates at the boundary between these phases. Calculations indicate the possibility of growing NCs with either pure zinc-blende or wurtzite structures. In essence, this study introduces new degree of freedom in the growth and application of GaN-based nanostructures grown via the vapor-liquid-solid method.