Non-equilibrium synthesis, structure, and opto-electronic properties of Cu2−2x Zn x O alloys

Alloying in traditional semiconductors is a well-established method to tune the electronic structure and the materials properties, but this technique is less common for oxides. Here, we present results on the non-equilibrium alloying of the prototypical semiconductor Cu2O with ZnO synthesized via high-throughput RF magnetron sputtering. It is demonstrated that the Zn solid solubility in Cu2O structure can be increased up to 17 at.% in the substrate temperature range 210–270 °C; this upper bound estimate of the solubility limit is much higher than that at equilibrium (sub atomic percent range). The preferential orientation in the film changes from (200) to (111) with increasing Zn concentration, but the lattice parameter and the grain size (80–180 nm) remains constant. Incorporation of Zn into Cu2O increases the optical absorption fourfold at the band gap (2.1 eV) and reduces the p-type electrical conductivity by an order of magnitude. The ability to synthesize phase pure Cu2−2xZnxO alloys with Zn solid solubility in excess of the thermodynamic limit with tunable structural and optoelectronic properties demonstrates the potential of non-equilibrium growth to overcome the solubility limits in oxide thin films and the promise of such alloys for optoelectronic applications.