Anisotropic optical and structural properties of hexagonal boron nitride epilayers probed by optical ellipsometry

Hexagonal boron nitride (h-BN) is a 2D layered material that has gained increasing attention in recent years due to its unique physical properties that make h-BN a promising material for DUV optoelectronics and solid-state neutron detectors. There are many material properties still uncertain, including h-BN’s optical constants. The anisotropic index of refraction of h-BN free-standing epilayers grown by metal organic chemical vapor deposition were measured using spectroscopic ellipsometry in the UV spectral range. It was found that the index of refraction for E⊥c-axis (ordinary) is much higher than E||c-axis (extraordinary). The scattered data for the index of refraction of h-BN reported earlier for various h-BN materials can be explained by including the inclination of turbostratic (t-) phase layers or the change of the c-plane orientation of individual layers. Our results show that ellipsometry can be used to characterize the crystalline quality of h-BN epilayers by determining the average inclined angle of t-phase layers within the sample while being non-invasive and highly sensitive.