Investigation of undoped and Tb-doped ZnO films on Al2O3 substrate by infrared reflection method

Undoped and Tb-doped ZnO thin polycrystalline films grown on Al2O3 substrate by magnetron sputtering approach were investigated using external infrared reflection in the spectral range from 50 to 5000 cm−1. The modelling of the IR reflection spectra was performed for absorbing film on semi-infinite substrate. For undoped ZnO film, the single oscillator model was used. Theoretical calculations were found to be in good agreement with the experimental results. The free carrier concentration, mobility and specific conductivity of electrons in ZnO films on Al2O3 substrates with E→⊥c→ orientation were determined. It was found that sheet resistance of the films investigated was much higher than that obtained from IR reflection spectra, which was ascribed to the presence of high resistive spaces between ZnO columns. In this case, IR reflection method is suitable for analysing the electrical parameters of textured materials when planar conductivity gives the incorrect results. Apparent effect of Tb doping on ZnO conductivity was not observed in the films investigated.