Gadolinium doping effect on SnO2 thin films optical and electrical properties

Abstract

Undoped SnO2 thin films, as well as Gd-doped SnO2 thin films, were deposited on glass substrate by spray pyrolysis technique. The effect of gadolinium concentration and substrate annealing on structural, optical and electrical properties of SnO2 films are investigated. The structural properties of these thin films were analyzed using x-ray diffraction (XRD). XRD analysis confirmed the polycrystalline tetragonal crystalline structure of the films with mainly (110) preferential growth plane. The crystallite size has been reduced from 35 nm to 15 nm with increasing Gd dopant concentration. The films optical transmittance spectra exhibit high transparency of about 76%–87% in visible region. The films optical gap is enlarged from 3.43 eV in the un-doped films to 3.71 eV when Gd doped. The films figure of merit revealed a maximum value of about 8.2 × 10–3(Ω/sq)−1 at 550 nm wavelengths. The highest conducting and transparency are obtained in the film prepared with 3 wt% Gd doping ratio. Hence, we conclude that 3 wt% ratio is the optimal one required for Gd:SnO2 film production that may found optoelectronic applications, in particular, as window layer in solar cells.