Sn–Ga co-doping in sol-gel derived ZnO thin films: Studies of their microstructural, optical, luminescence and electrical properties

Abstract

Sn–Ga co-doped ZnO films with different proportions synthesized by the sol-gel spin-coating technique have been investigated for their microstructural, optical, luminescence, and electrical properties using a variety of characterization techniques. All the films exhibit c-axis orientation along the (0 0 2) plane having a hexagonal wurtzite structure of zinc oxide. The crystallinity of the films improves upon doping and co-doping. Morphological images reveal that the films possess the granular morphologies with varying features. The co-doped films have a higher root mean square (RMS) roughness in comparison to the undoped and doped ZnO films. In general, relative to the undoped film, the transmittance of the film improves upon doping and co-doping. The direct energy band-gap has a maximum value of 3.26 eV for the undoped ZnO film, which decreases upon doping and co-doping. In the visible region, the refractive index exhibits a minimum value of 2.12 for the 1T3GZO film at the wavelength of 600 nm. The photoluminescence spectra of the films consist of one near-band edge (NBE) emission peak related to the recombination of free excitons, and a few broad emission peaks linked to the native defects in the films. Among the co-doped ZnO films, the 1 at% Sn–Ga co-doped film (1T1GZO) has the optimum transmittance and electrical conductivity.