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

Highlights: ► The influence of the technological factors on the dielectric dispersion of the zinc oxide thin films with nanograins was investigated. ► The dielectric dispersion of nanostructured zinc oxide films at frequency range of 4 Hz–100 kHz was observed. ► The nature of relaxation process is connected with space-charge polarization on the grain boundary, of the nanostructured zinc oxide. ► The substrate temperature during deposition of the transparent zinc oxide films affects on the structural, electrical, and optical properties of synthesized 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 4 Hz–100 kHz and temperature range of 120–380 K 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 573 K, whereas the second sample was manufactured without substrate heating. We observed the relaxation process in these materials at the temperature range of 220–350 K within the above mentioned frequency window. The second relaxation process was recognized in the frequency range of 100 kHz–2 MHz in vicinity of 350 K. The specific dispersion connected with a piezoelectric effect in the first sample was observed in vicinity of 215 K. 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.