Epitaxial growth and characterization of gan thin films on 2D MoS2 substrates via plasma-assisted molecular beam epitaxy

Abstract

Gallium nitride (GaN) is an excellent material for high-performance optoelectronic and power electronic devices due to its superior thermal conductivity and exceptional electron transport properties. However, growing high-quality GaN films is challenging because of lattice mismatch and thermal expansion coefficient differences with conventional substrates like sapphire and silicon, resulting in threading dislocations and structural defects that compromise device performance. This study addresses these issues by utilizing a 2D-MoS₂ buffer layer, which provides an atomically smooth surface and quasi-van der Waals interface to minimize lattice mismatch stress and suppress defect propagation. GaN thin films were grown on MoS₂-deposited c-sapphire substrates using plasma-assisted molecular beam epitaxy (PA-MBE) under optimized conditions. The MoS₂ layer was prepared using a chemical vapor deposition process followed by nitridation. Characterization techniques, including Reflection High-Energy Electron Diffraction, Atomic Force Microscopy, Field Emission Scanning Electron Microscopy, and X-ray Diffraction, confirmed that the GaN films exhibited high crystallinity, phase purity, and preferred c-axis orientation, with minimal structural defects. Surface analysis showed moderate roughness, with a root mean square value of 11.35 nm, attributed to localized growth variations. The MoS₂ buffer layer significantly reduced lattice mismatch-induced stress, as indicated by the absence of secondary phases in XRD analysis and facilitated defect-free epitaxial growth. These findings demonstrate the transformative potential of combining PA-MBE with 2D material buffers to achieve high-quality GaN films. This approach holds promise for optoelectronic applications such as LEDs and laser diodes, as well as high-frequency electronic devices like high-electron-mobility transistor