Tailoring optical properties of pulsed laser deposition grown epitaxial SrTiO3 thin films by tantalum doping

Abstract

The tunability of both optical bandgap and refractive index of the films is crucial for designing the next generation light emitting devices, lasers, power electronics, and transparent electronics. These applications, however, require high optical transparency along with reduced Fresnel reflection losses, which can be achieved through lower refractive indices at the interfaces. Here, we report on the growth of epitaxial SrTi1−xTaxO3 (x = 0–0.05) thin films via pulsed laser deposition and shed light on the modulation of their optical properties by analyzing their optical transparency and refractive index. Prior to the optical characterization, the epitaxial nature and structural properties of the films are examined by high-resolution x-ray diffraction. The SrTiO3 (STO) films are further investigated by x-ray absorption fine structure at the Ti K-edge to understand the change in local structures and electronic properties under varying Ta concentrations. Using a combination of spectroscopic ellipsometry and ultraviolet–visible spectroscopy, the effect of Ta doping on the optical properties of the films is revealed. The behavior of Ta doping on STO is studied theoretically using density functional theory, and the results corroborate the experimental values. The combined theoretical and experimental results provide strong evidence on the influence of Moss–Burstein shift, bandgap renormalization, and free electron carrier concentration on the optical bandgap of STO, and these findings can be explored further for different applications.