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

Micron-thick BN films are prepared on 2 in. c-plane sapphire substrates using low-pressure halide vapor phase epitaxy, with BCl3 and NH3 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.