Growth and Characterization of Off-Stoichiometric LaVO$_3$ Thin Films

TL;DR

This study investigates how off-stoichiometry in LaVO₃ thin films, achieved by varying growth conditions, affects their structural, optical, and electronic properties, revealing significant deviations from bulk behavior and phase transitions.

Contribution

It provides new insights into how stoichiometric deviations influence LaVO₃ thin films' properties, highlighting the role of structural distortions and lattice parameters in electronic phase behavior.

Findings

Off-stoichiometry alters structural distortion levels.

La-rich films show electronic phase separation.

V-rich films behave as Mott insulators.

Abstract

LaVO$_3$ (LVO) has been proposed as a promising material for photovoltaics because its strongly correlated \textit{d} electrons can facilitate the creation of multiple electron-hole pairs per incoming photon, which would lead to increased device efficiency. In this study, we intentionally grow off-stoichiometric LVO films by changing the growth conditions such as laser fluence. Our aim is to study how deviating La:V stoichiometries affect the electronic properties of LVO thin films. We find that the off-stoichiometry clearly alters the physical properties of the films. Structural characterization shows that both La-rich and V-rich films have different levels of structural distortion, with La-rich (V-rich) films showing a larger (smaller) out-of-plane lattice parameter compared to what one would expect from epitaxial strain effects alone. Both types of films show deviation from the behavior of bulk LVO in optical measurement, i.e., they do not show signatures of the expected long range orbital order, which can be a result of the structural distortions or the presence of structural domains. In transport measurements, La-rich films display clear signatures of electronic phase separation accompanying a temperature induced metal-insulator transition, while V-rich films behave as Mott insulators. The out-of-plane lattice parameter plays a crucial role in determining the transport properties, as the crossover from Mott-insulating to disorder-induced phase-separated behavior occurs around a lattice parameter value of 3.96 $\overset{\circ}{\mathrm{A}}$, quite different from what has been previously reported.