Effect of Growth Induced (Non)Stoichiometry on the Structure, Dielectric Response, and Thermal Conductivity of SrTiO3 Thin Films

We report dramatic variations in cation stoichiometry in SrTiO3 thin films grown via pulsed laser deposition and the implications of this nonstoichiometry for structural, dielectric, and thermal properties. The chemical composition of SrTiO3 thin films was characterized via X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. These studies reveal that deviations in laser fluence and deposition geometry can result in deviations of cation stoichiometry as large as a few percent. Additionally, X-ray diffraction was used to probe structural evolution and revealed an asymmetric strain relaxation mechanism in which films possessing Sr-excess undergo relaxation before those possessing Sr-deficiency. Furthermore, the dielectric constant decreases and the loss tangent increases with increasing nonstoichiometry with intriguing differences between Sr-excess and -deficiency. Thermal conductivity is also found to be sensitive to nonstoichiometry, with Sr-excess and -deficiency resulting in 65% and 35% reduction in thermal conductivity, respectively. These trends are explained by the expected defect structures.