Polarized Reflectance Spectroscopy and Spectroscopic Ellipsometry Determination of the Optical Anisotropy of Gallium nitride on Sapphire

The refractive indices n ⊥( E ⊥c) and n ∥ ( E ∥c) of the hexagonal GaN on sapphire substrates have been determined in the transparent region using the polarized reflection measurements. It is found that the difference in the refractive indices for E ⊥c and E ∥c is below 3% over the entire wavelength range measured, and ε ∞, the high-frequency dielectric constant, is 5.14 for E ⊥c and 5.31 for E ∥c. Ellipsometry angles, Δ and Ψ, have been calculated using the results of n ⊥, n ∥ and the thickness of the film, and an excellent agreement has been obtained between the calculated results and ellipsometric measured data.