Preparation and characterization of ZnO and doped-ZnO thin films by electrospraying method at atmospheric pressure for transparent electrode applications

Abstract

ZnO and Al-doped ZnO thin films were fabricated by electrospraying method at atmospheric pressure followed by annealing. The effects of annealing and Al doping on the structural, electrical and optical properties of the films were examined. The results show that films have random orientation with compact hexagonal wurtzite structure. It also implies that the annealing and the Al doping help to improve the electrical conductivity and optical properties as well. The minimum value of resistivity was 1.65 x 10-4 Ω cm for 0.5 at. % Al-doped ZnO film and transmittance was greater than 91 % in the visible region. The present value of resistivity is comparable to the lowest values for Al-doped ZnO films reported in open literatures. All the films prepared by this method have a good crystalline structure and homogenous surface. At atmospheric pressure, the electrospraying method was confirmed to be suitable for the preparation of Al-doped ZnO films with low resistivity and high transmittance. Two emission bands were observed in the PL spectra; one was located in the UV range and the other one comprise of green luminescence. Metal-doped (B and Ta) ZnO thin films were deposited by the electrospraying method onto a heated glass substrate. The structural, electrical and optical properties of the films were investigated as a function of dopant concentration in the solution and also as a function of annealing temperature. The results show that all the prepared metal-doped ZnO films were polycrystalline in nature with a (0 0 2) preferred orientation. Heat treatment of the films enhanced the transmittance, Hall mobility, carrier concentration and crystallinity. It was also examined that 2 at.% is the optimal doping amount in order to achieve the minimum resistivity and maximum optical transmittance. The annealing of the as-deposited thin films in air resulted in the reduction of resistivity. Depending on the characteristics of dopant, mainly ionic radius, the effects of dopan...