# Direct epitaxial growth of polar (1-x)HfO2-(x)ZrO2 ultra-thin films on Silicon

## TL;DR

This study demonstrates the direct epitaxial growth of polar (1-x)HfO2-(x)ZrO2 thin films on silicon substrates, revealing phase stabilization mechanisms and expanding integration possibilities for ferroelectric materials.

## Contribution

It introduces a novel pulsed laser deposition method enabling epitaxial growth of polar HfZrO2 films directly on silicon, with in situ native oxide scavenging.

## Key findings

- Polar phases coexist with monoclinic phases depending on substrate orientation.
- Epitaxial polar phases are stabilized by interfacial strain and native oxide layers.
- The work provides insights into phase stabilization conditions for ferroelectric thin films.

## Abstract

Ultra-thin Hf1-xZrxO2 films have attracted tremendous interest owing to their Si-compatible ferroelectricity arising from polar polymorphs. While these phases have been grown on Si as polycrystalline films, epitaxial growth was only achieved on non-Si substrates. Here we report direct epitaxy of polar phases on Si using pulsed laser deposition enabled via in situ scavenging of the native a-SiOx under ballistic conditions. On Si (111), polar rhombohedral (r)-phase and bulk monoclinic (m-) phase coexist, with the volume of the former increasing with increasing Zr concentration. R-phase is stabilized in the regions with a direct connection between the substrate and the film through the compressive strain provided by an interfacial crystalline c-SiO2 layer., The film relaxes to a bulk m-phase in regions where a-SiOx regrows. On Si (100), we observe polar orthorhombic o-phase coexisting with m-phase, stabilized by inhomogeneous strains at the intersection of monoclinic domains. This work provides fundamental insight into the conditions that lead to the preferential stabilization of r-, o- and m-phases.

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Source: https://tomesphere.com/paper/1907.06097