Morphology Evolution of a h-BN Film Grown by Halide Vapor Phase Epitaxy at Different Growth Temperatures

Abstract

Micron-thick BN films are prepared on 2 in. c-plane sapphire substrates using low-pressure halide vapor phase epitaxy, with BCl 3 and NH 3 being utilized as the respective sources of boron and nitrogen. The morphology and crystal quality of BN films grown at temperatures ranging from 1050 to 1650 °C are systematically investigated. X-ray diffraction analysis demonstrates that the synthesized films are primarily oriented along the [0002] direction of hexagonal boron nitride (h-BN), although a small amount of turbostratic BN is also observed. Scanning electron microscopy measurements reveal a typical layered stacking morphology in the cross section of h-BN films. As the growth temperature rises, h-BN has a tendency to transition from a 3D to a 2D growth mode, as seen by the coalescence of h-BN nanograins to form smooth micron-scale triangular grains. Transmission electron microscopy characterization shows that these triangular grains are well-crystallized [0002]-oriented h-BN phases, with minor variations in crystallographic orientations among individual grains. While these micron-scale triangular grains have not yet coalesced into larger grains, further refinement of the growth conditions holds the potential to induce their coalescence, resulting in the formation of continuous thick h-BN films with high crystal quality.