Significant role of substrate temperature on the morphology, electronic structure and thermoelectric properties of SrTiO3 films deposited by pulsed laser deposition

Abstract

The effect of substrate temperature on the surface morphology, electronic structure, and thermoelectric properties of SrTiO3 (STO) films were investigated using the atomic force microscopy, X-ray diffraction, X-ray absorption spectroscopy (XAS). The STO films were grown by pulsed laser deposition by varying the substrate temperatures from room temperature to 850 °C. A strong dependence of the lattice parameters and the surface morphology lead to the 3D island growth process with substrate temperature. The variation in the substrate temperature results in the evolution of the microstructure and the enhancement of electrical and thermoelectric properties. The large power factor of 10 μWm−1K−2 at (400 K) is evident for the thin films deposited at the substrate temperature of 650 °C and is highly suitable for thermoelectric applications. The XAS spectra reveal the reduction in valence state and off-center displacement of Ti ions in TiO6 octahedron with substrate temperatures. These spectra shift to the lower energy side indicating the presence of oxygen vacancies that are responsible for the observed transport behaviour. These results show that the substrate temperature plays a significant role in tuning the electrical and thermoelectric properties due to O vacancies. Thus, the optimum growth temperature required for the deposition of the SrTiO3 films is 650 °C for thermoelectric applications.