Rotationally Aligned Hexagonal Boron Nitride on Sapphire by High-Temperature Molecular Beam Epitaxy

TL;DR

This paper demonstrates the growth of high-quality, rotationally aligned hexagonal boron nitride on sapphire substrates using ultra-high temperature molecular beam epitaxy, achieving smooth, layered films suitable for technological integration.

Contribution

It presents a novel method for growing high-crystalline-quality, rotationally aligned hBN on sapphire via MBE at high temperatures, with detailed structural characterization.

Findings

High-quality hBN grown at >1600°C and low boron flux

hBN layers exhibit 60° rotational symmetry and specific crystallographic alignment

Films are smooth, layered, and few nanometers thick

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.