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.

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.