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 equilib- rium (sub atomic percent range). The preferential orienta- tion 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 con- ductivity by an order of magnitude. The ability to synthe- size phase pure Cu2-2xZnxO alloys with Zn solid solubility in excess of the thermodynamic limit with tunable struc- tural and optoelectronic properties demonstrates the potential of non-equilibrium growth to overcome the sol- ubility limits in oxide thin films and the promise of such alloys for optoelectronic applications.