The effect of electronegativity difference on the defect chemistry in lone-pair semiconductors

Abstract Whereas metal additives, incorporated in lone-pair semiconductors as positively charged centres, act like ionized donors, electronegative additives which possess lone-pair electrons give rise to centres which can be in either one of three charge states, negative, neutral, and positive. As a consequence, oxygen or halogen additive may give rise to a complete set of Street-Mott gap states. These are shifted towards lower electron, energies with respect to the states of intrinsic valence alternation centres because of the larger electronegativity of the additives. The addition of oxygen or halogen may lead to an increase or a decrease of the electrical conductivity depending on the relative values of the average carrier excitation energies.