Unveiling hidden charge traps in SrTiO3: TiSr antisite defects

In oxide-based electronic systems, polar point defects act as charge traps and strongly influence the electrical properties of these systems. While cation antisite defects are commonly present in oxides and give rise to intriguing physical phenomena such as ferroelectricity, spin ordering, and cathodoluminescence, their fundamental charge trapping characteristics remain elusive. Herein, we demonstrate that antisite Ti defects (Ti_Sr) can serve as significant charge traps in SrTiO₃ (STO). The formation of Ti_Sr defects was precisely controlled by adjusting the cation stoichiometry of STO, as verified by low-temperature photoluminescence and Raman spectroscopy. The charge trapping of Ti_Sr defects was then directly examined through low-frequency noise measurements of ultrathin SrRuO₃ (SRO) channels, which were in-situ grown on the stoichiometry-controlled STO. The SRO channel on STO films with a higher density of Ti_Sr defects shows a unique feature of two Lorentzian noise components, while that on stoichiometric STO exhibits a typical 1/f-type noise. Our analysis of the thermal activation process reveals that Ti_Sr defect-induced charge trapping can occur with a quite low activation energy of ∼0.044 eV due to interfacial band shift. These results suggest that cation-related point defects, which have previously been underestimated, can significantly impact the electronic properties of oxide-based electronic systems.