The change of electrical transport characterizations in Ga doped ZnO films with various thicknesses

GZO films with different thicknesses were prepared at room temperature by magnetron sputtering and the structure is characterized using two-dimensional X-ray diffraction along with transmission electron microscope and X-ray photoelectron spectroscopy. The films show a textured orientation along the c-axis and an average transmittance of over 90%. The films of 100 and 200 nm are characterized by a semiconductor behavior in the temperature range of 80–320 K, while the conduction behavior turns into a metallic transport at 160 K as the film thickness increases to 400 nm. Temperature dependence of the conductivity manifests a weak localization effect dominated in the semiconductor behavior. The transition between semiconductor and metallic behavior with increasing the thickness is shown to be associated to crystallinity of the films which is improved with decreasing defects and lattice distortion. It is suggested that the improvement of crystallinity should be favored by reduction of the weak localization effect and in turn enhance the semiconductor-to-metal transition.