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 (~3.3eV), 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.