Cation nonstoichiometry and its impact on nucleation, structure and defect formation in complex oxide heteroepitaxy : LaCrO3 on SrTiO3(001)

TL;DR

This study investigates how cation nonstoichiometry affects the growth, structure, and defect formation in LaCrO3 thin films on SrTiO3(001), revealing the importance of stoichiometry control for device fabrication.

Contribution

It provides new insights into the effects of cation stoichiometry on film quality, interface mixing, and defect formation in complex oxide heteroepitaxy using molecular beam epitaxy.

Findings

La-rich films have lower structural quality than Cr-rich films.

Cation mixing occurs at the interface regardless of stoichiometry.

La indiffusion into SrTiO3 is promoted by substrate defects.

Abstract

Our ability to design and fabricate electronic devices with reproducible properties using complex oxides is critically dependent on our ability to controllably synthesize these materials in thin-film form. Structure-property relationships are intimately tied to film and interface composition. Here we report on the effects of cation stoichiometry in LaCrO3 heteroepitaxial films prepared using molecular beam epitaxy. We show that LaCrO3 films grow pseudomorphically on SrTiO3(001) over a wide range of La-to-Cr atom ratios. However, the growth mode and structural quality are sensitive to the La-to-Cr ratio, with La-rich films being of considerably lower structural quality than Cr-rich films. Cation mixing occurs at the interface for all La-to-Cr ratios investigated, and is not quenched by deposition at ambient temperature. Indiffused La atoms occupy Sr sites in the substrate. The presence of defects in the SrTiO3 substrate is implicated in promoting La indiffusion by comparing the properties of LaCrO3/SrTiO3 with those of LaCrO3/Si, both prepared at ambient temperature. Additionally, pulsed laser deposition is shown to result in more extensive interfacial mixing than molecular beam epitaxy for deposition at ambient temperature on Si.