Influence of technological factors on conductivity and dielectric dispersion in ZnO nanocrystalline thin films

Abstract

Influence of the technological factors such as annealing of a substrate on the dielectric dispersion of the zinc oxide thin films with nanograins was investigated. In the first stage the dielectric dispersion of such nanostructured zinc oxide films at frequency range of 4Hz–100kHz and temperature range of 120–380K was studied. The two types of films were prepared by the RF-magnetron sputtering in argon atmosphere using ZnO targets. The first sample was obtained by sputtering on the substrate heated to 573K, whereas the second sample was manufactured without substrate heating. We observed the relaxation process in these materials at the temperature range of 220–350K within the above mentioned frequency window. The second relaxation process was recognized in the frequency range of 100kHz–2MHz in vicinity of 350K. The specific dispersion connected with a piezoelectric effect in the first sample was observed in vicinity of 215K. The value of dielectric permittivity reaches 1100 at frequencies of few Hertz and decreases with increase of measuring electric field frequency. The nature of the low-frequency relaxation process is connected with space-charge polarization on the grain boundary. It is realized due to the high defect concentration within the interfaces of the ZnO nanograins in comparison with a bulk material. The high-frequency relaxation process corresponds to the thermal dipole polarization involving electrons localized at oxygen vacancies.