Using atom probe tomography to understand Schottky barrier height pinning at the ZnO:Al / SiO2 / Si interface

TL;DR

This study investigates the Fermi level pinning at ZnO:Al / SiO2 / Si interfaces using atom probe tomography and electronic transport, revealing that Al segregation and the insulator-metal transition influence Schottky barrier behavior.

Contribution

It demonstrates that Al segregation causes metallic behavior at the interface, linking Fermi level pinning to the insulator-metal transition in doped ZnO.

Findings

Schottky barrier height remains constant despite doping variations

Al segregates to the interface, likely forming a metallic layer

Fermi level pinning may be related to the insulator-metal transition

Abstract

We use electronic transport and atom probe tomography to study ZnO:Al / SiO2 / Si Schottky junctions on lightly-doped n- and p-type Si. We vary the carrier concentration in the the ZnO:Al films by two orders of magnitude but the Schottky barrier height remains constant, consistent with Fermi level pinning seen in metal / Si junctions. Atom probe tomography shows that Al segregates to the interface, so that the ZnO:Al at the junction is likely to be metallic even when the bulk of the ZnO:Al film is semiconducting. We hypothesize that Fermi level pinning is connected to the insulator-metal transition in doped ZnO, and that controlling this transition may be key to un-pinning the Fermi level in oxide / Si Schottky junctions.