Band alignment of AlxGa1–xN/Cu2O heterojunctions in dependence on alloy composition x and its effect on the photovoltaic properties

The band alignment of p-Cu2O/n-AlxGa1–xN heterojunction with x up to 0.15 was studied by X-ray photoelectron spectroscopy. The conduction band offset between binary Cu2O and ternary AlxGa1–xN is found to decrease with increasing x. The data suggest that a flatband situation in the conduction band of p-Cu2O/n-AlxGa1–xN heterojunctions can be achieved for x about 0.4, which is an Al-content where n-type doping is still feasible. Thus, n-AlxGa1–xN with x between 0.4 and 0.6 may be a suitable window material for heterojunction solar cells with a p-Cu2O absorber layer. The current-voltage characteristics of the p-Cu2O/n-AlxGa1–xN heterojunctions under illumination confirm the anticipated improvement of the photovoltaic properties with increasing x.