Optical properties of sputtered amorphous beryllium nitride thin films

Abstract

The optical properties of amorphous beryllium nitride (a-Be3N2) thin films deposited on Si (100) at temperature <50°C using reactive rf sputtering deposition were examined in the wavelength range of 280–1600nm. X-ray diffraction of the films showed no structure, suggesting the Be3N2 films grown on the Si (100) substrates are amorphous. The thicknesses and optical constants of the films were derived from variable-angle spectroscopic ellipsometry measurements using the Cauchy-Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range n=1.98–2.28 and κ=0.0002–0.08, respectively. Analysis of the absorption coefficient shows the optical absorption edge of a-Be3N2 films to be 4.12±0.01eV. These values were in excellent agreement with the photoluminescence measurements (4.18eV). The surface morphology was characterized by atomic force microscopy. The surfaces of the films were very smooth and their average roughnesses were measured to be in the range of 0.36–2.4nm. An effective medium approximation model of 50% Be3N2 and 50% voids was used in the ellipsometric fitting procedure. The spectral dependence of transmissivity of the films was investigated at different angles of incidence (20°–80°). The a-Be3N2 films shown high transmissivity (80%–99%) in the visible and near infrared regions.