INFLUENCE OF THE ALUMINUM DOPING ON THE KINETIC PROPERTIES OF ZINC OXIDE THIN FILMS

Abstract

The results of the dispersion of optical functions and optical constants studies for zinc oxide thin film doped with aluminum are presented. The deposition of Al-doped ZnO (2.5 wt.%) thin films are performed by magnetron sputtering. Al-doped ZnO thin film crystallizes in hexagonal structure (structure type - ZnO, space group P6₃mc (No. 186), with the unit-cell dimensions a= 3.226(2) Å and c= 5.155(6) Å (V= 46.49(6) ų). Optical transmittance spectra (300–2500 nm) showed that the Al-doped ZnO thin film is of high optical quality and value of optical bandgap (3.26 eV) is very close to undoped samples. The study of optical functions is performed on the basis of the experimentally measured transmission spectrum using the bypass method. The spectral behavior of optical functions: refractive index, extinction coefficient, absorption index, dielectric functions and optical conductivity are established. The value of Urbach's energy and the dependence of oscillator strength on the size of the bandgap and the concentration of doping element are determined. Observed is the increase of the Urbach’s energy for Al-doped ZnO thin film in comparison to the undoped ones. The almost double increase of the optical oscillator strength value has been revealed for the thin film studied. The influence of aluminum doping on the dynamic change of optical mobility, optical resistance and relaxation time is established for the first time for studied compound. Also, the value of the plasma frequency is determined and its correlation with the carrier density is defined. The doping of ZnO thin films with aluminum leads to the increase of the optical mobility, relaxation time and plasma frequency that was revealed by comparison with reference data for the undoped ZnO. Due to good optical properties, this thin film is good candidates as materials for optoelectronic devices.