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

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 H-2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2x10(-4) Omega cm. The carrier concentration increased with increasing H-2 concentration during deposition. X-ray diffraction results showed that the d(0002) interplanar spacing increased with increasing H-2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 degreesC during deposition. Both results suggested that the increase of carrier concentration by adding H-2 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 H-2 composition. The phenomenon is interpreted as the filling of conduction band by electrons in n-type semiconductor. (C) 2004 American Institute of Physics.