Schottky barrier heights at polar metal/semiconductor interfaces

TL;DR

This study uses first-principle calculations and a linear-response model to analyze how Schottky barrier heights vary at polar metal/semiconductor interfaces, considering surface termination and chemical composition.

Contribution

It introduces a simple, accurate model for barrier-height variations based on linear-response theory and atomic-scale computations extending classical image charge concepts.

Findings

Barrier heights are higher for anion-terminated surfaces.

Barrier variations depend on semiconductor chemical composition.

Classical image charge concepts extend to atomic-scale distances.

Abstract

Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.