Optical properties of GaN by using ellipsometry and a band calculation

We present the optical properties of a hexagonal GaN (alpha-GaN) film grown on a c-plane (0001) sapphire substrate with about a 1.9-mu m thickness. The pseudodielectric function spectra of GaN were obtained from 0.7 to 9.0 eV at room temperature by using vacuum UV-variable angle spectroscopic ellipsometry. To determine the exact critical point (CP) energy values, we used a parametric semiconductor model and a standard line shape analysis for 2nd derivatives of GaN data. Also, from the obtained CP values, we calculated the band structures of GaN by using the linear augmented Slater-type orbital (LASTO) method to identify the CPs.