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

摘要

The copper oxides cuprite (Cu_2O) 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-Ga_2O_3 and β-Ga_2O_3, 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 Cu_2O/α-Ga_2O_3 heterostructure appears to offer the most favorable band alignment for photovoltaic applications.