Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, epsilon(1)(E) + i epsilon(2)(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E perpendicular to c at angles of incidence of 60 degrees and 65 degrees with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n(2)(lambda) = 1 + 1.881 lambda(2)/(lambda(2) - 0.0538(2)). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge. (C) 1998 American Institute of Physics. [S0003-6951(98)01725-2].