Optical functions of uniaxial ZnO determined by generalized ellipsometry

The optical functions of uniaxial ZnO have been determined using two-modulator generalized ellipsometry, where a single measurement is sufficient to determine the optical functions from appropriately aligned uniaxial crystals. Above the direct band edge (similar to 3.3 eV), this technique produces the most accurate values of the optical functions of ZnO presently available, while the refractive indices determined below the direct band edge agree with minimum-deviation methods. Near the direct band edge, the optical functions are modified by the excitonic interaction with a three-dimensional critical point. The optical dielectric response functions are fit to a recent formulation by Holden et al. [Phys. Rev. B 56, 4037 (1997)]. One isotropic point in the spectrum was observed at 3.114 eV, and a near-isotropic point near 3.31-3.34 eV.