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