Comparison of transparent conductive oxide thin films prepared by a.c. and d.c. reactive magnetron sputtering

Abstract

Antimony-doped tin oxide and aluminum-doped zinc oxide films have been prepared by reactive a.c. and d.c. magnetron sputtering (a.c. excitation at frequency of 40 kHz; twin-cathode arrangement) from metallic targets at substrate temperature of about 573 K. The optical, electrical and structural properties of the sputtered SnO 2:Sb and ZnO:Al thin films of different dopant concentrations have been investigated by means of optical spectroscopy (UV-IR), X-ray diffraction. Hall mobility and conductivity measurements. For antimony-doped SnO 2 films a minimum resistivity of 1.5 × 10 −3 Ω cm at high transparency (larger than 88% at film thickness of 250 nm) has been observed at dopant concentrations of about 1.2 at.% Sb in the layers. Low resistivity of 4.0 × 10 −4 Ω cm and transmission in the visible spectral range of about 89% at film thickness of 550 nm has been obtained for as prepared aluminum-doped ZnO thin films. Furthermore, the investigations on a.c. plasma discharges using a planar plasma probe analyzer have revealed higher ion energies (up to some tenths of eV) and about 10 times higher ion current densities as in the case of d.c. magnetron sputtering at nearly the same deposition conditions.