Characterization of ZnO structures by optical and X-ray methods

ZnO thin films doped by Ga and In as well as multilayer structures of ZnO/Al2O3 have been investigated by X-ray fluorescence, Raman spectrometry, spectroscopic ellipsometry and vacuum ultra violet reflectometry. Systematic changes in the optical properties have been revealed even for Ga concentrations below 1%. The Raman active phonon mode of Ga doping at 580 cm-1 shows a correlation with the Ga concentration. Optical models with surface nanoroughness correction and different parameterizations of the dielectric function have been investigated. There was a good agreement between the dielectric functions determined by the Herzinger-Johs polynomial parameterization and by direct inversion. It has been shown that the correction of the nanoroughness significantly influences the accuracy of the determination of the layer properties. The band gap and peak amplitude of the imaginary part of the dielectric function corresponding to the excitonic transition changes systematically with the Ga-content and with annealing even for low concentrations.