Fabrication and properties of pure-phase Cu2O co-doped with zinc and indium

Cuprous oxide (Cu2O) thin films co-doped with zinc (Zn) and indium (In) were fabricated with direct current (DC) magnetron sputtering. The sputtering voltage of the Cu target was fixed while that of the alloy target of Zn and In was varied. It is found that when the alloy target voltage is below 310 V, pure-phase Cu2O can be obtained while a further increase in the alloy target voltage will result in the presence of metallic copper. The surface morphologies, the atomic ratios of the Zn and In, and the grain size do not have a linear dependence on the sputtering voltage of the alloy target. Higher concentration doping will decrease the lattice constant of Cu2O. Pure-phase samples doped with Zn and In have relatively higher transmittance and larger optical band gaps. The n-type conduction of Cu2O co-doped with Zn and In is realized when the sputtering voltage of the alloy target is 310 V. Zn and In atoms are found to exist as Zn2+ and In3+ in the films and they are possible donors for the n-type conduction.