Effect of oxygen flow rate ratio on crystalline phase and properties of copper oxide films prepared by room-temperature high-power impulse magnetron sputtering

Copper oxide films were prepared at room temperature using high-power impulse magnetron sputtering (HiPIMS). The oxygen flow rate ratio in the Ar/O-2 mixture plasma gas is varied from 1.0% to 3.0% and its influences on the plasma radicals, growth mechanism and film properties are systematically investigated. The crystal phase of the film strongly depends on the oxygen flow rate ratio as indicated by the XRD and XPS results. The films consist of mixed (Cu + Cu2O) phase when deposited with an oxygen flow rate ratio of 1.0-2.5%. The Cu2O fraction increases with oxygen flow rate ratio and reaches the greatest value at 2.5%. A n-type to p-type conductivity transition is observed at around 2.0% due to the increasing Cu2O fraction. A phase transition to CuO is observed at a higher oxygen flow rate ratio of 3.0%. The phase transition and conductivity type transition occurred at a much lower oxygen flow rate ratio but similar O-2 partial pressure when compared with those reported in literature, implying that the O-2 partial pressure is the critical quantity for reactive sputtering rather than the O-2 flow rate ratio. Crucially, the film deposited with 2.5% oxygen flow rate ratio exhibits the highest hole mobility of 32 cm(2)/V.s, the lowest hole concentration of 4.0 x 10(15) /cm(3), the highest transmittance and the largest band gap of 2.62 eV. The film is potential to be used as the channel material of transparent p-type field effect transistors. The results may be helpful for the preparation of copper oxide film by HiPIMS for application in optoelectmnic devices.