Inverse design approach to hole doping in ternary oxides: Enhancing p-type conductivity in cobalt oxide spinels

Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresponding p-type doping in wide-gap insulators, while maintaining transparency, has proven difficult. Here, by utilizing design principles distilled from theory with systematic measurements in the prototype A(2)BO(4) spinel Co(2)ZnO(4), we formulate and test practical design rules for effective hole doping. Using these, we demonstrate a 20-fold increase in the hole density in Co(2)ZnO(4) due to extrinsic (Mg) doping and, ultimately, a factor of 10(4) increase for the inverse spinel Co(2)NiO(4), the x = 1 end point of Ni-doped Co(2)Zn(1-x) Ni(x)O(4).