The structure and properties of copper oxide and copper aluminium oxide coatings prepared by pulsed magnetron sputtering of powder targets

Abstract

The development of p-type semiconductors is one of the key technologies for p–n junction-based devices, such as diodes, transistors and light-emitting diodes. Copper oxide and copper aluminium oxide (CuAlO 2) coatings are known to show p-type conductivity and, as a consequence, these materials are attracting increasing attention. In this study, therefore, various copper oxide and CuAlO 2 films were deposited by pulsed magnetron sputtering from loosely packed powder targets, formed from either Cu 2O powder alone, or blends of Cu 2O and Al 2O 3 powders, in a rig specifically designed for the purpose. The coatings were deposited at varying partial pressures of oxygen and then annealed at atmospheric pressure. The optical, electrical and structural properties were determined using a range of techniques including spectrophotometry, four-point probe, scanning electron microscopy and X-ray diffraction. Analysis of the films showed that, in the former case, crystalline Cu 2O and CuO structures could be produced, depending on the oxygen partial pressure during deposition and the post-deposition annealing conditions. The as-deposited Cu 2O films were found to have a very high optical transmittance in the visible range with up to 95% transmission. In comparison, the CuO films showed lower transmittance in the visible range, but greater transmittance in the IR range. The optical band gaps obtained from the transmittance and reflectance measurements were 2.44 and 1.78 eV for Cu 2O and CuO, respectively. The CuAlO 2 coatings were also found to be crystalline, with optical and electrical properties again dependant on the deposition and annealing conditions. The direct deposition of transparent conductive oxide films from loosely packed powder targets by pulsed magnetron sputtering is a novel, highly versatile technique for the deposition of this type of material.