Highly flexible van der Waals thin films from direct hetero-epitaxial growth

Abstract

We present hetero-epitaxial thin films of a single crystal gallium nitride on fluorophlogopite mica (F-mica) without buffer layers. It employs quasi-van der Waals epitaxy to directly grow GaN thin films on flexible substrates, thus integrating 2D layered materials with conventional semiconductor to achieve highly flexible van der Waals thin films. The nitridation and annealing atmosphere are critical on the direct growth of GaN films on substrates via quasi-van der Waals epitaxy. Specifically, we demonstrate that surface modification of F-mica through annealing under NH₃ atmosphere to form a nanoscale nitride layer, which supports the hetero-epitaxy without buffer layers. Our research highlights that this modified F-mica substrate provides superior nucleation sites and smoother surface characteristics, leading to the growth of GaN thin films with lower dislocation densities and improved structural integrity. This innovative approach not only simplifies the hetero-epitaxial growth process but yields GaN crystals suitable for high-performance flexible electronic and optoelectronic devices. Our findings generalize a substantial pathway in the fabrication of highly flexible semiconductor thin films on 2D materials, leveraging the unique properties of 2D materials and quasi-van der Waals epitaxy to achieve superior material performance. It supports the advancements of next-generation 2D materials formation and flexible devices.