Optical Properties and Interband Transitions of ZnO and Cu-doped ZnO Films Revealed by Spectroscopic Ellipsometry Measurement

摘要

Optical properties analysis of ZnO and Cu-doped ZnO films on Pt substrate have been probed by using Spectroscopic Ellipsometry (SE) at room temperature. Here, we study the optical transitions and the evolution of excitonic states by means of the critical points (CP) analysis. The second derivative spectra of dielectric function (CP analysis) show the transition of excitonic peak at the fundamental absorption edge (E_0). Corresponds to ε_1 spectra, the peak of refractive index (n) at around 3.3 eV is broaden by introducing Cu dopant. This peak is assigned as excitonic states and the peak broadening is mainly due to the screening of excitons. This excitonic screening is more pronounced in the second derivative spectra of dielectric function where the peaks intensity is decreased upon Cu dopant. In additions, effective number of carrier concentrations of ZnO film shows a high number as high as ~10~(22) cm~(-3). Furthermore, the addition of Cu doping -in this case 8 in at.%- does not significantly affect the effective number of ZnO film carrier concentration. This result confirms the strong interaction between ZnO film and Pt substrate and negligible contribution of Cu dopant for carrier concentration.