Modeling of electrochemical oxide film growth -- impact of band-to-band tunneling

TL;DR

This paper extends the Point Defect Model for oxide film growth by including electron and hole transport and band-to-band tunneling, revealing that BTBT is rare and electric field buffering occurs without constant field assumptions.

Contribution

The study introduces a more complex model incorporating electron/hole transport and BTBT, challenging the assumption of constant electric field in oxide film growth modeling.

Findings

BTBT occurs only in narrow band gap and high electric field cases

Electrons and holes buffer the electric field but do not maintain it constant

Including charge carrier transport is crucial for narrow band gap oxide films

Abstract

The Point Defect Model (PDM) describes the corrosion resistance properties of oxide films based on interfacial reactions and defect transport, which are affected by the electric field inside the oxide film. The PDM assumes a constant electric field strength due to band-to-band tunneling (BTBT) of electrons and the separation of electrons and holes by high electric fields. In this manuscript we present a more complex expansion of the common models to simulate steady state oxide films to test this assumption. The R-PDM was extended by including the transport of electrons and holes and BTBT. It could be shown that BTBT only occurs in very rare cases of narrow band gaps and high electric fields and the impact of electrons and holes does indeed lead to a buffering effect on the electric field, but does not lead to a constant electric field strength. Modeling the transport of electrons and holes on the oxide film allows to specifically estimate their potential impact on the film growth. Especially during modeling of oxide films with narrow band gap and/or electrochemical reactions at the film/solution interface the electrons and holes needs to be included to the model.