SrTi_1-xTa_xO₃(x = 0-0.1) epitaxial thin films for next generation transparent electronics

Cubic SrTiO₃ is one of the most used indirect band gap (3.2 eV) oxide semiconductors. It displays many exotic properties, i.e., transparent conductivity, photocatalysis, ferroelectricity, two-dimensional electron gas, etc. due to the manipulations of defect chemistry and constituent elements via impurity doping.  Here, we report on the complexity of the optoelectronic and structural properties of the epitaxially stabilized 0-10 at.% Ta-doped SrTiO₃ (001) thin films on LaAlO₃ (001) substrates by selectively  varying the growth temperature (650-850 °C) and oxygen partial pressure (5×10^-2 - 5×10^-7 mbar) during the pulsed laser deposition using a 248 nm excimer laser with an energy density of 1.5 J/cm² at the repetition rate of 5 Hz.  These films are characterized by high-resolution XRD, RBS-channelling, AFM, UV, HR-XPS and electrical measurements. All the films are found to be epitaxial in nature, stoichiometric composition, excellent uniformity in thickness and transparent in the UV region. The effect of growth parameters and Ta dopant on the epitaxial quality of these layers are understood by determining the dopant location and its concentration in the SrTiO₃ lattice. The expansion of the lattice parameter of SrTiO₃ with Ta concentration is explained by computational modelling. The complex relationships of optical and electronic properties on growth parameters, dopant concentration, and single crystal quality of the films are also found. Metallic properties in the film enhance with decreasing pO₂ and increasing growth temperature. The obtained room-temperature resistivity, carrier density, and mobility from the optimized sample turn out to be ∼5×10⁻³ Ω cm, 2.63×10²⁰/cm³, and 4.5 cm² /V s, respectively and high optical transparency ∼85%–90%, offer it as an exciting material for next generation transparent optoelectronics.