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.