The role of the band gaps in reconstruction of polar surfaces and interfaces

TL;DR

This paper investigates how band gaps influence the electronic reconstruction mechanisms in polar surfaces and interfaces, using DFT calculations on MgO to understand electrostatic potential compensation.

Contribution

It reveals the limiting role of the band gap in free-standing films and how band alignment in heterostructures alters reconstruction pathways.

Findings

Electronic reconstruction is limited by the band gap in free-standing films.

Residual electric fields are sensitive to tiny electron transfer deviations.

Band alignment in heterostructures changes the electronic compensation mechanisms.

Abstract

Density functional theory applied to a simple ionic material, MgO, is used as a model system to clarify several aspects of electronic driven mechanism to compensate for the diverging electrostatic potential in the polar structures. We demonstrate that in the stoichiometric free standing films, the electronic reconstruction is limited by the band gap. This produces a residual electric field in the bulk of the sample which is extremely sensitive to tiny deviations in electron transfer between two surfaces of the slab. In heterostructures, the band gap is replaced by a new effective energy scale set by the band alignment of its component. This changes the reconstruction pathways so that the electronic mechanism can benefit from the smallest energy scale possible.