Optical modulation of Gate-Induced Electron Trapping via Persistent Photoconductivity in STO/Al Heterostructures

Abstract: The dynamic interplay between light and electric field control of charge states lies at the heart of developing multifunctional optoelectronic devices. While persistent photoconductivity (PPC) and gate-voltage (VG)-induced electron trapping are well-known phenomena in oxide heterostructures, their mutual coupling remains poorly explored. Here, we report that the non-equilibrium state established by PPC can effectively modulate the efficacy of VG-induced electron trapping in a STO/Al heterostructure. The PPC, characterized by a slow relaxation (8.5 hours at 4 K) after sub-illumination, originates from the re-trapping of photoexcited carriers into deep-level states. In contrast, VG-induced trapping, governed by shallow states, exhibits much faster dynamics ({100 - 400 s). Crucially, we discover that the strength of VG-induced trapping is not constant but is dynamically modulated by the PPC relaxation process. The trapping amplitude is strongly amplified after illumination and recovers only after the deep-level states are substantially refilled, precisely following the PPC relaxation time constant. Furthermore, the electron trapping effect diminishes with increasing temperature and vanishes near the ferroelastic phase transition of STO (110 K), confirming that ferroelastic twin walls and associated oxygen vacancy clusters are the physical origin of the traps. Our findings reveal a novel optical gating mechanism for electron trapping, paving the way for designing non-volatile, optically programmable electronic devices.