Artificial Aging of Thin Films of the Indium-Free Transparent Conducting Oxide SrVO₃

Abstract

SrVO3 (SVO) is a prospective candidate to replace the conventional indium tin oxide (ITO) among the new generation of transparent conducting oxide (TCO) materials. In this study, the structural, electrical, and optical properties of SVO thin films, both epitaxial and polycrystalline, are determined during and after heat treatments in the 150–250 °C range and under ambient environment in order to explore the chemical stability of this material. The use of these relatively low temperatures speeds up the natural aging of the films and allows following the evolution of their related properties. The combination of techniques rather sensitive to the film surface and of techniques sampling the film volume will emphasize the presence of a surface oxidation evolving in time at low annealing temperatures, whereas the perovskite phase is destroyed throughout the film for treatments above 200 °C. The present study is designed to understand the thermal degradation and long-term stability issues of vanadate-based TCOs and to identify technologically viable solutions for the application of this group as new TCOs.

Formation and Etching of the Insulating Sr‐Rich V5+ Phase at the Metallic SrVO3 Surface Revealed by Operando XAS Spectroscopy Characterizations

“…[ 50,51 ] Therefore, both XPS and XAS results point to the presence of a mostly stoichiometric SrVO 3 surface after 1 min of water bath, sufficient to fully remove the chemically modified aged surface. As shown in, [ 36 ] we can consider the thickness of the removed top layer to be 3 nm thick, resulting in an etching rate of 0.05 nm s −1 , consistent with what reported in literature. [ 39 ]…”

“…[50,51] Therefore, both XPS and XAS results point to the presence of a mostly stoichiometric SrVO 3 surface after 1 min of water bath, sufficient to fully remove the chemically modified aged surface. As shown in, [36] we can consider the thickness of the removed top layer to be 3 nm thick, resulting in an etching rate of 0.05 nm s −1 , consistent with what reported in literature. [39] In order to follow the cleaning process during the measurement, we slow down the speed of the reaction by fluxing 3% of water vapor in 50 sccm of He atmosphere under ambient pressure for 130 min.…”

“…The relatively low annealing temperature used to speed up the aging barely affects SVO crystallinity. [36] At the NFFA APE-HE beamline of the Elettra synchrotron radiation facility, [40] XPS measurements were then performed in UHV with linearly polarized radiation of 900 eV photon energy, corresponding to a probing depth of ≈1 nm. The photoemission spectra were measured at room temperature (RT), with the sample surface oriented at 45° with respect to the incident photon beam and normal to the analyzer axis.…”

“…All these thermodynamic instabilities near the surface result in a stoichiometric modification of the material, which is detrimental for its use in both Mottronic applications and as TCO due to the increase in resistivity. [19,30,36] In this framework, the focus of recent studies was dedicated to the removal of this spurious surface layer to restore the stoichiometric properties. Most of the Sr compounds are soluble in liquid water but with very different rates, much faster for the Sr-rich phases.…”

“…All these thermodynamic instabilities near the surface result in a stoichiometric modification of the material, which is detrimental for its use in both Mottronic applications and as TCO due to the increase in resistivity. [ 19,30,36 ]…”