Optical modulation of gate-induced electron trapping via persistent photoconductivity in SrTiO3/AlOx 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 SrTiO3/AlOx heterostructure. After the cessation of light illumination, the decay of PPC shows a slow relaxation with time constant τl = 9 h at 4 K, which originates from the re-trapping of photoexcited carriers into deep level states. In contrast, the electron trapping induced by the application of VG is governed by shallow states and exhibits much faster dynamics (τ ∼ 100 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. Furthermore, the electron trapping effect diminishes with increasing temperature and vanishes near the ferroelastic phase transition of SrTiO3 (∼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 that may inspire future designs of optically programmable oxide electronics.