Compositional Design of Non-Stoichiometric Gallium Oxide Thin Films

Abstract

The study investigates the influence of an unexplored severe oxygen deficiency on the electrical transport properties of non-stoichiometric gallium oxide thin films, which are promising candidates for resistive switching in memristors. We employed pulsed-laser deposition to grow oxygen-deficient gallium oxide thin films on c-cut sapphire single-crystal substrates at 400 °C, with O/Ga ratios varying depending on the growth conditions. Increasing the laser fluence in vacuum (2 × 10–7 mbar) leads to a decrease in the O/Ga ratio from 1.3 to 0.8, resulting in anomalous low-temperature transport behavior. X-ray photoelectron spectroscopy revealed three chemical states for Ga, indicating oxygen deficiency, metallic Ga nanoclusters, and a gallium oxide matrix. The highly non-stoichiometric amorphous Ga2Ox thin films exhibit metastable behavior, consisting of metallic Ga nanoclusters embedded in a gallium oxide matrix, explained by a solid-state disproportionation reaction. The temperature-dependent electrical resistivity of the films between 4 and 300 K exhibited metallic and semiconducting behavior as a function of the O/Ga ratio, coupled in few cases with partial or complete superconducting transitions in the range from 5 to 6.3 K. These results contribute to the development of nanostructured materials with tailored electrical properties for advanced neuromorphic applications and quantum computing.