Electronic origins of p-type transparent conductivity in SrCu2O2

Abstract

SrCu2O2 retains the p-type conductivity of Cu2O while exhibiting a pronounced upward shift of the conduction band minimum (CBM), enhancing visible-light transparency. This CBM upshift is commonly attributed to weakened Cu-3d/Cu-3d coupling induced by Sr-O bonding. However, such an interpretation is inconsistent with the widely accepted Cu-4s dominated character of the CBM. Using first-principles calculations, we find that the CBM is primarily dominated by Cu-3d orbitals with Cu-4s hybridization, rather than being purely Cu-4s in nature. The elevated CBM arises from weakened bonding coupling between the Cu-4s/O-2p and the Cu-3d/Cu-3d antibonding states. Defect calculations indicate that Cu and Sr vacancies generate ultra-shallow acceptor levels but exhibit high formation energies, limiting intrinsic hole concentrations. In contrast, K doping produces low-energy KSr acceptors with readily ionizable levels, enabling hole concentrations exceeding 1018 cm−3 under annealing at 500 K. This study provides a revised electronic-structure picture of the optical transparency of SrCu2O2 and proposes K doping as an effective strategy for enhancing its performance in transparent electronic applications.