Giant bulk photovoltaic effect in an iron-based magnetic semiconductor.

Abstract

Efficient bulk photovoltaic (BPV) conversion and room-temperature ferromagnetism are difficult to combine, because the itinerant electrons that support magnetic order favor metallic transport, whereas BPV generation requires a semiconducting state with broken inversion symmetry. Here, we show that oxygen-plasma implantation transforms metallic Fe₃GaTe₂ into a ferromagnetic semiconductor with a giant BPV response, enabling zero-bias photocurrent generation in a non-centrosymmetric lattice. Oxygen incorporation localizes itinerant Fe d-electrons, induces p-type semiconducting transport and polar electronic structure, while oxygen-associated exchange pathways allow persistent ferromagnetic state above room temperature. The resulting devices exhibit spontaneous broadband photoresponse, with short-circuit current densities approaching 30 A cm^-2 and a BPV coefficient up to 0.25 V^-1. The photovoltaic current can be linearly programmed by low magnetic fields based on field-dependent magnetoresistive modulation. Using the experimentally calibrated device response, we demonstrate magnetically programmable feature separation and image restoration with 92.3% recognition accuracy, establishing oxygen-engineered Fe₃GaTe₂ as a platform for self-powered, reconfigurable magnetic optoelectronics.