Giant persistent photoconductivity in electron-doped SrTiO3 triggered by release of electron-lattice coupling

Strontium titanate has emerged as a promising material for oxide-based electronics due to its versatile electronic properties and compatibility with cation doping. This study investigates the giant persistent photoconductivity (PPC) in ultrathin La-doped SrTiO₃ (La:STO) films. We demonstrate that, unlike conventional PPC mechanisms based on oxygen vacancies, a strong and robust PPC can be triggered by activating electrons localized at Ti ions near the surface of La:STO films, where electron-lattice coupling plays a pivotal role. Specifically, for the 8-unit-cell-thick La:STO films, the Ti-related PPC of 1,276% is achieved under exposure to ultraviolet (UV) light with a wavelength of 405 nm. This PPC state remains highly stable, with full release taking more than 24 h at room temperature. Our first-principles density functional theory calculations and thickness-dependent photocurrent analysis consistently reveal that this giant PPC originates from electrons activated at Ti³⁺O₆ octahedra located near the surface of the La:STO layer. These results demonstrate that electron-lattice interactions in transition metal oxides can give rise to strong PPC characteristics, suggesting future applications in low-dimensional optoelectronic devices.