Optimized two-step growth of large surface two-dimensional boron nitride on Ge (001) films by molecular beam epitaxy

The growth of two-dimensional boron nitride (2D-BN) thin films on Ge (001) has been studied, with the ultimate goal of integrating this material into Si technology. Molecular beam epitaxy was used in a dedicated ultra-high vacuum chamber. To avoid the formation of thermal pits on heating the Ge film above ∼750 °C, a two-step procedure was optimized. A thin 2D-BN buffer layer is first grown at ∼730 °C using two independent cells for B and N, aimed at stabilizing the Ge surface and to prevent thermal pits formation upon further heating. The second-step at 800 °C makes use of another precursor, gaseous borazine, in the same chamber. The growth proceeds in a step-flow mode, and results in homogeneous nano-crystalline large-surface 2D-BN films with a ∼1 nm roughness.