Effect of Ga doping on microstructure, morphology, optical and electrical properties of spray deposited CdO thin films

Abstract

Cadmium oxide (CdO) and gallium (Ga) doped CdO thin films were fabricated successfully onto glass substrate at 400 °C temperature by spray pyrolysis technique and the effect of Ga on microstructure, surface morphology, optical, electrical and Hall effect properties of CdO thin films have been revealed and discussed. X-ray diffraction results indicate that all films are polycrystalline and possess cubic crystal structure. The SEM images reveal that the surface morphology of CdO changes remarkably with increasing Ga doping concentration. EDX investigation confirms the presence of cadmium (Cd), oxygen (O) and gallium (Ga) elements in the deposited films. The optical transmittance of CdO increases continuously with Ga doping up to 3% and then decreases onwards within the same wavelength region. The optical band gap initially increases from 2.47 eV to 2.53 eV, and Urbach energy decreases from 0.55 eV to 0.50 eV when the doping of Ga varies from 0 to 3%. Thereafter, the extinction coefficient, refractive index and energy dissipation factor shows reverse relation above 3% doping of Ga. The electrical resistivity of CdO thin film has been found 5.79 × 10−4 (ohm-cm) and which reduces to 1.23 × 10−4 (ohm-cm) for 3% Ga doping. The temperature dependent electrical resistivity data of deposited films shows that the films possess poor metal-like behaviour. Results of Hall Effect measurement notifies that the carrier of the films is n-type, and Ga doping changes the Hall mobility & carrier concentration of CdO films significantly. The obtained figure of merit of all films is higher than 1.0% Ω−1 and the maximum FOM was found for 3% (8.28 %Ω−1) Ga doped CdO films.