Determining the band alignment of copper-oxide gallium-oxide heterostructures.

The copper oxides cuprite (Cu2O) and tenorite (CuO) are ideal candidates for solar cells as they promise high conversion efficiencies according to the Shockley–Queisser limit. However, both cannot readily be doped n-type, thus hampering the formation of all copper oxide p–n junctions for solar cell applications. The combination of the copper oxides with gallium sesquioxide, in particular, α-Ga2O3 and β-Ga2O3, is considered to be an excellent heterojunction system for overcoming this challenge. In such a p–n junction, the p-type copper oxide layer will act as an absorber and the transparent n-type gallium sesquioxide will act as a window layer. In these devices, the band alignment at the internal interface is crucial for the device performance. Here, we study the band alignments of four different copper oxide–gallium sesquioxide heterostructures by x-ray photoelectron spectroscopy. Within the experimental margin of error, a Cu2O/α-Ga2O3 heterostructure appears to offer the most favorable band alignment for photovoltaic applications. [ABSTRACT FROM AUTHOR]