Structure, conductivity, and transparency of Ga-doped ZnO thin films arising from thickness contributions

Abstract

Ga-doped ZnO (GZO) films were deposited on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. It is revealed that the influence of deposition parameters, such as target-substrate distance and deposition time, on the structure and properties of the films arises primarily from the variations in film thickness. For the GZO films with smaller thicknesses (≤385 nm), crystallinity is greatly improved with an increase in thickness, which leads to an increase in Hall mobility and a decrease in electrical resistivity. The carrier concentration is, however, found to exhibit only a slight change with the thickness variations. The relationship of electrical property and microstructure suggests that the resistivity of the films arises mainly from ionic impurity scattering rather than from grain boundary scattering. All the films exhibit a transmittance of over 90% in the visible wavelength range. The band gap of the GZO films is widened with increasing film thickness. In combination with the result that the carrier concentration exhibited a slight dependence on thicknesses, the broadening of the band gap with thicknesses is attributed more to the improved crystallinity than to the Moss–Burstein shift.