Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering

Abstract

Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4Ωcm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorption increased with increasing H2 composition. The phenomenon is interpreted as the filling of conduction band by electrons in n-type semiconductor.