Control of microstructure by using self-buffer layer and its effects on properties of Ga-doped ZnO thin films deposited by radio frequency magnetron sputtering

• The effects of microstructure and defects have been investigated separately.
• The control of c-axis orientation by inserting a self-buffer layer.
• The reduction of grain boundary contribution to Hall mobility on well oriented films.
• The improvement of in-grain properties by post deposition annealing.

In this study, the influence of microstructure on the properties of Ga-doped ZnO (GZO) films deposited by radio frequency magnetron sputtering was investigated by a combination of microstructural control and post-deposition annealing. GZO films deposited on bare glass substrates at room temperature (RT) showed poor c-axis orientation; however, insertion of a thin GZO layer deposited at 200 °C as a self-buffer layer resulted in high c-axis orientation. Regardless of the microstructure, the carrier concentration, Hall mobility, and optical transmittance of the GZO film deposited at RT were lower than those of the GZO film deposited at a higher substrate temperature of 200 °C, because of the presence of defects in the former film. The carrier concentration and optical transmittance of both the GZO film with the self-buffer layer and the GZO film without the self-buffer layer increased after the post-deposition annealing. However, a significant improvement of the Hall mobility was observed only for the highly c-axis oriented GZO films deposited on the self-buffer layer. Evaluation of the contribution of grain boundary scattering to the Hall mobility by employing optical mobility as the measure demonstrated that the contribution of grain boundary scattering clearly existed in the case of the GZO films without the self-buffer layer but it was almost negligible in the case of well-oriented GZO films deposited on the self-buffer layer.