Transition-Metal Impurities in Semiconductors—Their Connection with Band Lineups and Schottky Barriers

The dependence of cation-substitutional transition-metal impurity levels upon the host semiconductor is calculated self-consistently in a defect-molecule approach. Heterojunction band lineups and Schottky-barrier heights can be calculated within the same tight-binding model. In all three systems, the characteristic behavior is determined by an approximate local charge-neutrality condition imposed by electrostatic self-consistency ("pinning"), with a dangling-bond level playing the role of the "neutrality level." In this way we explain the observed correlation between transition-metal impurity levels, heterojunction band lineups, and Schottky barriers.