Comparison of radio-frequency and direct-current magnetron sputtered thin In 2O 3 : Sn films

Abstract

Polycrystalline In 2O 3 : Sn films have been prepared by direct-current (dc) and radio-frequency (rf) magnetron sputtering at 300 °C substrate temperature and analyzed by optical transmittance spectra, X-ray diffraction spectra and atomic force micrography. The optical and electronic properties of the samples were derived from a simulation of the transmittance spectra based on dielectric modeling. Generally, the rf-sputtered films have larger lattice distortion, microstrain and a lower carrier density than the dc-sputtered films. The predominant orientation of rf-sputtered films is (222), instead of the (400) orientation found for dc-sputtered films. Contrary to dc-sputtering, there was no clear influence of the oxygen partial pressure on the texture of rf-sputtered films. A grain–subgrain structure was sometimes observed and correlated with the texture of both rf- and dc-sputtered films. Correlations between surface roughness, crystal lattice expansion and packing density are observed. The experimental results are explained by oxygen interstitials forming acceptor centers and different plasma parameters for rf- and dc-sputtering. The electron mobility in all samples is quantitatively explained by scattering at ionized donors and donor–acceptor complexes.