High-Crystallinity and High-Temperature Stability of the Hexagonal Boron Nitride Film Grown on Sapphire

Hexagonal boron nitride (hBN) as an ultrawide bandgap semiconductor has great potential for being fabricated into optoelectronics used in the deep ultraviolet (DUV) spectral region. A high-crystallinity hBN film has been achieved on a catalyst-free sapphire substrate by using the LPCVD technique, where the nitridation process plays a key role in obtaining high-quality hBN featuring suppressive N-vacancy. Such an epitaxial hBN film on sapphire has shown an initially flat surface with trench topography, then evolves to a honeycomb-corrugated surface, and finally demonstrates a nanocrystalline surface with increasing growth pressure. This morphology evolution implies a step-flow growth model and the generation of local stresses on sapphire. We have proposed a growth mechanism for hBN grown on sapphire; namely, boron (B)-oxygen (O) chemical bonds initially formed provide effective nucleation sites, leading to the formation of circle-like hBN islands, which play an important role in maintaining the high-temperature stability of hBN at 1200 degrees C after being stored in the atmosphere. This work paves an effective way for achieving high-quality hBN grown at ultrahigh temperatures, on which any further device structure can be subsequently deposited due to its high-temperature stability.