Role of substrate induced electron-phonon interactions in biased graphitic bilayers

TL;DR

This paper investigates how substrate-induced electron-phonon interactions affect the bandgap in biased graphitic bilayers, revealing that these interactions generally widen the gap and depend on lattice structure and bias strength.

Contribution

It provides a perturbative analysis of electron-phonon interactions in various lattice configurations, highlighting their impact on bandgap tuning in graphitic bilayers.

Findings

EPIs tend to widen the bandgap in ionic bilayers.

The effect of EPIs varies with lattice structure and bias magnitude.

Large bias reduces the impact of EPIs on the bandgap.

Abstract

Bilayers of graphitic materials have potential applications in field effect transistors (FETs). A potential difference applied between certain ionic bilayers made from insulating graphitic materials such as BN, ZnO and AlN could reduce gap sizes, turning them into useful semiconductors. On the other hand, opening of a small semiconducting gap occurs in graphene bilayers under applied field. The aim here is to investigate to what extent substrate induced electron-phonon interactions (EPIs) modify this gap change. We examine EPIs in several lattice configurations, using a perturbative approach. The typical effect of EPIs on the ionic bilayers is an undesirable gap widening. The size of this gap change varies considerably with lattice structure and the magnitude of the bias. When bias is larger than the non-interacting gap size, EPIs have the smallest effect on the bandgap, especially in configurations with $AA^{\prime}$ and $AB$ structures. Thus careful selection of substrate, lattice configuration and bias strength to minimise the effects of EPIs could be important for optimising the properties of electronic devices. We use parameters related to BN in this article. In practice, the results presented here are broadly applicable to other graphitic bilayers, and are likely to be qualitatively similar in metal dichalcogenide bilayers such as MoS$_2$, which are already of high interest for their use in FETs.