Unified interface dipole theory for Fermi level pinning effect at metal-semiconductor contacts

TL;DR

This paper introduces a unified bond dipole theory combining first-principles and tight-binding methods to explain Fermi level pinning at metal-semiconductor interfaces, emphasizing the role of surface dangling bonds.

Contribution

It presents a comprehensive microscopic model linking interface dipoles and Fermi level pinning through bond orbital interactions, unifying various interface states as a single bonding mechanism.

Findings

Localized bonding causes large interface dipoles and strong FLP.

Surface dangling bond density controls FLP strength.

The model explains differences in pinning between ionic and covalent semiconductors.

Abstract

We present a unified bond dipole theory for metal-semiconductor interfaces to explain the microscopic origin of interface dipoles and Fermi level pinning (FLP) in terms of Harrison's bond-orbital model. By combining first-principles calculations with tight-binding analysis, we show that localized bonding between semiconductor surface dangling bonds and metal orbitals is sufficient to generate a large interface dipole and induce strong FLP, even when only a single metal monolayer is present. Within this framework, metal-induced gap states (MIGS), dangling-bond-induced surface states (DBSS), and bonding states embedded in the valence band are all understood as different outcomes of the same underlying interface bonding mechanism, rather than as independent causes of FLP. We further establish that the key parameter governing FLP strength is the density of surface dangling bonds that can form new chemical bonds with the metal, which directly controls the magnitude of the bond-induced interface dipole. This picture naturally explains the weaker pinning observed in more ionic semiconductors than in covalent ones and provides practical guidance for engineering metal-semiconductor interfaces and tuning Schottky barrier heights.