  In this paper, oxidation of Cu during physical sputtering deposition in a
high purity and low pressure Ar atmosphere without introducing O2 gas flow was
studied systemically. It was found that various flexible Cu-based films could
be obtained by simply adjusting deposition parameters. Electrical and optical
testing results showed that the achieved pure Cu films and Cu+Cu2O composite
films both presented an intriguing combination of metal and semiconductor
characteristics. It is expected that such Cu-based films with a superior
conductivity and a solar-window bandgap may have fascinating potential
applications such as in high electron mobility transistors, electrodes and
solar cells. Further, the oxidation mechanisms of Cu under different deposition
parameters and the main O2 source during physical sputtering deposition were
also explored.
