Strong Asymmetrical Doping Properties of Spinel CoAl2O4

Using first-principles density-functional theory, we have investigated the intrinsic and extrinsic doping properties of CoAl ₂O ₄ by calculating the transition energies and formation energies of intrinsic and extrinsic defects. We find that CoAl ₂O ₄ exhibits strong asymmetrical doping properties: Although excellent p-type conductivity can be achieved by Li or Na doping at O-rich growth condition, n-type conductivity cannot be achieved by any intrinsic or extrinsic dopants at any growth conditions. These asymmetrical doping properties are attributed to the formation of intrinsic defects, particularly Al _Co, which has very low formation energy at all growth conditions. Our results suggest that for better use of CoAl ₂O ₄, the electronic devices should require CoAl ₂O ₄ to exhibit p-type conductivity.