OPTICAL FUNCTIONS OF UNIAXIAL ZNO DETERMINED BY GENERALIZED ELLIPSOMETRY

The optical functions of uniaxial ZnO have been determined using two-m odulator generalized ellipsometry, where a single measurement is suffi cient to determine the optical functions from appropriately aligned un iaxial crystals. Above the direct band edge (similar to 3.3 eV), this technique produces the most accurate values of the optical functions o f ZnO presently available, while the refractive indices determined bel ow 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 diel ectric response functions are fit to a recent formulation by Holden et al. [Phys. Rev. B 56, 4037 (1997)]. One isotropic point in the spectr um was observed at 3.114 eV, and a near-isotropic point near 3.31-3.34 eV.