Van der Waals Epitaxy of 2D Gallium Telluride on Graphene: Growth Dynamics and Principal Component Analysis

A scalable epitaxy of 2D layered materials and heterostructures constitutes a crucial step in developing novel optoelectronic applications based on high-crystalline quality 2D materials. Here, the formation of continuous, strain-free, high-crystalline quality 2D hexagonal gallium telluride (h-GaTe) directly on epitaxial graphene using molecular beam epitaxy is demonstrated. Morphological and structural characterizations evidence a coherent layer at the heterostructure interface having an in-plane lattice constant of 4.05 ± 0.01  $\dot{A}$ . The few-layer thick graphene determines the epitaxial registry of the h-GaTe with grains of sixfold symmetry and a multilayer-type homoepitaxial growth. Deposition temperature- and time-dependent surface topography indicate that the interlayer diffusion of adatoms plays a crucial role in achieving smooth GaTe films. Contrastive principal component analysis allows for screening large in situ diffraction data as a function of growth parameters. In this way, the trajectory of the 2D h-GaTe growth is mapped through phase space. These results are relevant for integrating epitaxial material in the fabrication of high-performance multifunctional devices.