Temperature Effect of van der Waals Epitaxial GaN Films on Pulse-Laser-Deposited 2D MoS2 Layer

Van der Waals epitaxial GaN thin films on c-sapphire substrates with a sp(2)-bonded two-dimensional (2D) MoS2 buffer layer, prepared by pulse laser deposition, were investigated. Low temperature plasma-assisted molecular beam epitaxy (MBE) was successfully employed for the deposition of uniform and similar to 5 nm GaN thin films on layered 2D MoS2 at different substrate temperatures of 500, 600 and 700 degrees C, respectively. The surface morphology, surface chemical composition, crystal microstructure, and optical properties of the GaN thin films were identified experimentally by using both in situ and ex situ characterizations. During the MBE growth with a higher substrate temperature, the increased surface migration of atoms contributed to a better formation of the GaN/MoS2 heteroepitaxial structure. Therefore, the crystallinity and optical properties of GaN thin films can obviously be enhanced via the high temperature growth. Likewise, the surface morphology of GaN films can achieve a smoother and more stable chemical composition. Finally, due to the van der Waals bonding, the exfoliation of the heterostructure GaN/MoS2 can also be conducted and investigated by transmission electron microscopy. The largest granular structure with good crystallinity of the GaN thin films can be observed in the case of the high-temperature growth at 700 degrees C.

Automated summary

Van der Waals epitaxial GaN thin films were successfully grown on c-sapphire substrates with a sp(2)-bonded two-dimensional MoS2 buffer layer. Higher substrate temperatures during molecular beam epitaxy (MBE) growth led to improved crystallinity and optical properties of the GaN films, as well as smoother surface morphology and stable chemical composition. Exfoliation of the GaN/MoS2 heterostructure was also examined, revealing the largest granular structures with good crystallinity in films grown at 700 degrees C.