# Graphene bandgap induced by ferroelectric Pca2$_1$ HfO$_2$ substrate: a first-principles study

## TL;DR

This study uses first-principles calculations to show that ferroelectric Pca2$_1$ HfO$_2$ substrates can induce a significant bandgap in graphene, with potential applications in graphene-based transistors.

## Contribution

It reveals how the ferroelectric Pca2$_1$ phase of HfO$_2$ can modify graphene's electronic properties, specifically inducing a tunable bandgap depending on surface termination.

## Key findings

- Graphene exhibits sizable energy gaps on ferroelectric HfO$_2$ substrates.
- Gap size varies with HfO$_2$ surface termination, larger for oxygen-terminated slabs.
- Orbital hybridization and structural deformation cause the bandgap opening.

## Abstract

The electronic properties of graphene on top of ferroelectric HfO$_2$ substrates in orthorhombic phase with space group Pca2$_1$ are investigated using density functional theory calculations. The space group Pca2$_1$ was recently identified as one of the two potential candidates for ferroelectricity in hafnia, with the polarization direction oriented along [001] direction. Our results indicate the appearance of sizable energy gaps in graphene induced by the HfO$_2$ substrate, as a consequence of orbital hybridization and locally deformed graphene structure. The gap sizes depend on the type of the HfO$_2$ terminations interacting with graphene, showing larger gaps for oxygen terminated slabs compared to hafnium terminated ones. These observations may prove to be highly significant for the development of graphene based field effect transistors using high-k dielectrics.