Aliovalent doping therefore produces a change in defect concentration that is proportional to the concentration of that defect species in the undoped material. Simple defect reaction schemes that assume that aliovalent doping is principally charge-compensated by forming additional charge-carrying mobile defects will therefore overestimate the effect of doping at some fixed concentration, unless the mobile defect species being targeted for enhancement is the dominant positively, or negatively, charged native defect species in the corresponding undoped system.