Limiting factor for electron mobility in sputtered Ga-doped ZnO thin films

Ga-doped ZnO (GZO) thin films were deposited on a glass substrate using RF-magnetron sputtering at various operating pressure and its electrical, structural and optical properties have been studied. In previous studies, resistivity was affected by both electron concentration and electron mobility, whereas in this study, resistivity was only controlled by electron mobility. Low operating pressure results in high conductivity due to high electron mobility. The enhanced electron mobility is attributed to the reduction in surface scattering by oxygen adsorption, which is a consequence of the reduction in the number of oxygen ions and the surface area. Under controlling the operating pressure, surface scattering exerts a more significant influence on electron mobility than grain-boundary scattering. The average transmittance (400-800 nm) was over 86% and increased with lower operating pressure. Therefore, the surface scattering plays a major role to achieve better electrical properties of GZO thin films sputtered under operating pressure conditions.