A germanate transparent conductive oxide

Wide bandgap conductors such as In₂O₃ and ZnO are used as transparent conducting oxides (TCOs). To date, TCOs are realized using post transition metal cations with largely spread s-orbitals such as In³⁺, Sn⁴⁺, Zn²⁺ and Cd²⁺. On the other hand, no good electronic conductor has been realized in oxides of Al, Si and Ge. Here we report the conversion of an oxide of Ge into a good electronic conductor by employing the concept of superdegeneracy. We find that cubic SrGeO₃, synthesized under high pressure, displays a direct bandgap of 3.5 eV, a carrier mobility of 12 cm²(Vs)⁻¹, and conductivities of 3 Scm⁻¹ (DC) and 400 Scm⁻¹ (optical conductivity). This is the first Ge-based electronic conductive oxide, and expands the family of TCOs from ionic oxides to covalent oxides.