POLARIZED REFLECTANCE SPECTROSCOPY AND SPECTROSCOPIC ELLIPSOMETRY DETERMINATION OF THE OPTICAL ANISOTROPY OF GALLIUM NITRIDE ON SAPPHIRE

The refractive indices n(perpendicular to)(E perpendicular to c) and n (parallel to) (E parallel to c) of the hexagonal GaN on sapphire subst rates have been determined in the transparent region using the polariz ed reflection measurements. It is found that the difference in the ref ractive indices for E perpendicular to c and E parallel to c is below 3% over the entire wavelength range measured, and epsilon(infinity), t he high-frequency dielectric constant, is 5.14 for E perpendicular to c and 5.31 for E parallel to c. Ellipsometry angles, Delta and Psi hav e been calculated using the results of n(perpendicular to), n(parallel to) and the thickness of the film, and an excellent agreement has bee n obtained between the calculated results and ellipsometric measured d ata.