Optical Properties of GaN Thin Films on Sapphire Substrates Characterized by Variable-Angle Spectroscopic Ellipsometry

Abstract

The optical properties of GaN thin films grown on sapphire substrates by low-pressure metal organic chemical vapor deposition were investigated by variable-angle spectroscopic ellipsometry. Accurate refractive indices ( n , k ) below, through, and above the fundamental bandgap of GaN in the spectra range of 1.5 to 3.8 eV (330 to 830 nm) were determined by using a parametric semiconductor model that took the surface roughness effect into account. The fundamental bandgap energy (3.41 eV) of GaN determined by the model was exactly the same as that obtained from an optical transmission experiment using the same sample. The high-frequency dielectric constant ε ∞ (=5.2) of GaN for ( E ⊥ c ) obtained from the ellipsometric measurement was also in excellent agreement with the experimental value of 5.2±0.1 ( E ⊥ c ) from the IR reflectivity measurements.