Cu-Doped Lithium Oxide Films with High Mobility and Bandgap Prepared by Pulsed Direct-Current Sputtering

Abstract

In this study, Cu-doped lithium carbonate (Cu:Li2O2) films are prepared by pulsed direct-current (DC) magnetron sputter using a lithium carbonate and copper oxide mixed target. The oxygen flow rate is varied during the sputtering process to systematically investigate its effect on structural, electrical and optical properties of the films. The experimental results show that all the Cu:Li2O2 films are mainly amorphous as confirmed by X-ray diffraction. Cu incorporation is able to reduce the aggregated clusters of the lithium oxides. At the oxygen flow rate of 20 sccm the film with a Cu content of ~0.65 at.% has a low p-type resistivity of 0.82 Ω-cm, hole concentration of 1.06×1017 cm-3 and the highest mobility of 73 cm2V-1s-1, which is at least twice higher than those of other p-type metal oxides prepared at similarly low temperatures. The film also has a high optical band gap of 2.87 eV. Moreover, the Cu:Li2O2/ZnO heterojunction demonstrating a clear diode rectification supports the p-type nature of Cu:Li2O2 films. The pulsed DC Cu:Li2O2 films with these remarkable optoelectronic properties demonstrate great potential to be adopted as transparent oxide semiconductors in high-performance optoelectronics.

Keywords: p-type, mobility, band gap, copper oxide, lithium oxide, pulsed DC