Optical anisotropy of wurtzite GaN on sapphire characterized by spectroscopic ellipsometry

Optical anisotropy of wurtzite GaN grown on sapphire was studied by spectroscopic ellipsometry (SE) over the wavelength range of 400-1200 nm at the incident angle of 68degrees. Both the dispersions of the refractive indices for E perpendicular to c (n(o)) and E parallel to c (n(e)) as well as the film thickness were determined by fitting SE measurement data with a suitable optical model. The average difference between the values of no and ne over the experimental wavelength range is 2.7%. To verify the results of SE measurements, the obtained values of n(o) were used to analyse the interference part of the UV-Vis reflection spectrum of GaN with near-normal incidence geometry and the film thickness was also calculated. The two thickness values obtained by SE and reflection spectra were in good consistence and the relative deviation was found to be only 0.16%.