The anisotropic index of refraction of 200 μm thick boron-10 enriched hexagonal boron nitride (h-BN) freestanding epilayers grown by metalorganic chemical vapor deposition has been measured using spectroscopic ellipsometry in the UV (4.0–5.1 eV) spectral range. It was found that the index of refraction for the polarization mode with an electric field perpendicular to the c-axis (ordinary, no) is much higher than that with an electric field parallel to the c-axis (extraordinary, ne). By inclusion of turbostratic- (t-) phase layers within h-BN having an average inclination angle (θ) with respect to the ideal c-plane, a simple method for quantifying θ has been deduced. Our results revealed that the presence of t-phase layers decreases the optical anisotropy of h-BN and that a signature of improved crystalline quality is an increase in the ordinary index of refraction (no) as a result of the average incline angle θ approaching 0° and predicted that no = 2.7 and ne = 1.5 at 280 nm for single crystalline h-BN epilayers. More importantly, our results demonstrated that spectroscopic ellipsometry is an effective technique for characterizing the crystalline quality of h-BN epilayers with the advantages of being noninvasive and highly sensitive.

Erbium nitride (ErN) is a rare-earth metal mononitride continuing to receive interest due to its unique electronic, magnetic, and optical properties. ErN has shown promise in the development of new functional materials for optoelectronic and spintronic devices. Here, we report on the optical properties of ErN crystals, grown by sublimation and probed by photoluminescence (PL) spectroscopy at both room temperature and 180 K. Multiple transition lines were observed between 2 and 4.5 eV. Using the PL results together with reported calculations, a coherent picture for the band structure at the Γ-point for ErN crystals was derived. PL results revealed that ErN has a minimum direct energy gap of 2.41 eV and a total of two valence bands and two conduction bands at the Γ-point separated by about 0.15 eV and 0.34 eV, respectively. These transitions reveal optical properties of ErN in the UV region and its band structure at the Γ-point.

Erbium nitride (ErN) is a rare-earth metal mononitride with desirable electronic, magnetic, and optical properties. ErN can be incorporated into III-nitride semiconductors to develop new functional materials for optoelectronic and spintronic devices. Here, we report on the optical properties of ErN crystals, grown by sublimation and probed by photoluminescence (PL) spectroscopy. Three transition lines were observed near 1 eV. Theoretically, ErN has a small indirect energy gap of around 0.2 eV with a conduction band minimum at the X-point of the Brillouin zone and a valence band maximum at the Γ-point. The predicted smallest direct energy gap is around 1 eV, with two valence bands at the X-point. Using the PL results together with the reported calculations, a coherent picture for the band structure at the X-point for ErN crystals has been derived. Experimental results revealed that ErN has a minimum direct bandgap of 0.98 eV and a total of two valence bands separated by about 0.37 eV at the X-point.