The chemical trends of limits to doping of many semiconducting metal oxides is analyzed in terms of the formation energies needed to form the compensating defects. The $n$-type oxides are found to have high electron affinities and charge neutrality levels that lie in midgap or the upper part of their gap, whereas $p$-type oxides have small photoionization potentials and charge neutrality levels lying in the lower gap. The doping-limit energy range is found to vary with the bulk free energy of the compound.

• Received 19 August 2010

DOI:https://doi.org/10.1103/PhysRevB.83.075205