Rotationally aligned hexagonal boron nitride on sapphire by high-temperature molecular beam epitaxy

Abstract

Hexagonal boron nitride (hBN) has been grown on sapphire substrates by ultra-high temperature molecular beam epitaxy (MBE). A wide range of substrate temperatures and boron fluxes have been explored, revealing that high crystalline quality hBN layers are grown at high substrate temperatures, $>$1600$^\\circ$C, and low boron fluxes, $\\sim1\\times10^{-8}$ Torr beam equivalent pressure. \\emph{In-situ} reflection high energy electron diffraction (RHEED) revealed the growth of hBN layers with $60^\\circ$ rotational symmetry and the $[11\\bar20]$ axis of hBN parallel to the $[1\\bar100]$ axis of the sapphire substrate. Unlike the rough, polycrystalline films previously reported, atomic force microscopy (AFM) and transmission electron microscopy (TEM) characterization of these films demonstrate smooth, layered, few-nanometer hBN films on a nitridated sapphire substrate. This demonstration of high-quality hBN growth by MBE is a step towards its integration into existing epitaxial growth platforms, applications, and technologies.