Epitaxy and Phase Stability of 2D Hexagonal Gallium Telluride on Silicon

Controlling crystal quality during epitaxial growth is essential for the advancement of novel materials with industrial relevance. Here, we investigate the molecular beam epitaxy of 2D hexagonal gallium telluride (h-GaTe) on silicon, focusing on the roles of substrate temperature, flux ratio, and surface treatment. Real-time monitoring through line-of-sight quadrupole mass spectrometry and reflection high-energy electron diffraction reveals a transition from 2D to 3D growth after the deposition of a critical number of layers, a process not attributable to strain relaxation. Structural and optical characterization by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence confirm the formation of large-area, high-crystalline-quality h-GaTe via van der Waals epitaxy. The thermal stability of h-GaTe was further assessed through systematic annealing, which revealed that the as-grown hexagonal phase undergoes amorphization followed by a transformation into an optically active, ordered phase at higher temperatures. These findings highlight the pathways to engineer 2D GaTe layers with controlled structure and properties, offering insights into their integration in next-generation optoelectronic devices.