Inverse design approach to hole doping in ternary oxides: Enhancing<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-type conductivity in cobalt oxide spinels

Abstract

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 ${A}_{2}B$O${}_{4}$ 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${}_{1\ensuremath{-}x}$Ni${}_{x}$O${}_{4}$.