Structural and optical behavior of gallium and cobalt co-doped ZnO thin films fabricated by a sol-gel spin coating technique

Abstract

In this study, the ZnO thin films with varying Ga/Co co-doping concentrations were produced on the quartz substrates by spin-coating technique. The structural and optical behavior of the films were analyzed by X-ray diffraction (XRD) and UV–Vis spectroscopy, respectively. XRD results reveal that all the films possess a hexagonal wurtzite structure of ZnO and have crystallite sizes in the range 8–24 nm. The prominent peaks (relative intensity greater than 10%) observed in the XRD profiles correspond to (100), (002), (101) and (103) planes, whereas the most preferred orientation of crystal growth in all the films is (002) plane. A small variation in the lattice constant values has been found owing to the inclusion of dopants and co-dopants in the ZnO lattice, as well as defects created in the crystal lattice at the time of film growth. Compared to the undoped ZnO film, the optical transmittance improves beyond the 430 nm wavelength upon 1 at% Ga doping, while in (1 at% Ga + 1 at% Co) and (3 at% Ga + 1 at% Co) co-doped films, it improves beyond the 600 nm wavelength. The UV–Vis spectroscopy results show the optical band gap value of 3.28 eV for the undoped ZnO film, which changes by a small amount in the doped and co-doped films.