Optical functions of uniaxial zinc oxide (ZnO) revisited

The optical functions of uniaxial ZnO are determined from 200 to 850 nm (6.2-1.46 eV) using three different ellipsometric techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE), (2) transmission two-modulator generalized ellipsometry, and (3) near-normal incidence two modulator generalized ellipsometry microscopy (2-MGEM). The 2-MGE results in very accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV, while the transmission 2-MGE results in more accurate values of the birefringence and associated errors below the band edge where ZnO is transparent. The 2-MGEM also measures the diattenuation (which is related to the birefringence) and other parameters, but at near-normal incidence at a single wavelength (577 nm). The 2-MGEM is designed as a scanning instrument resulting in these parameters being measured over a surface.