Valence band modification of Cr2O3 by Ni-doping: creating a high figure of merit p-type TCO

Abstract

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr₂O₃. Conductivities as high as 28 S cm⁻¹ were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr₂O₃ contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr₂O₃. Furthermore, it is experimentally proven that Ni has a higher solubility in Cr₂O₃ than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr₂O₃ than Mg and explains the improved conductivity observed for the former.