Vacancy Engineering Induces Spin-Polarized Photocurrent in Two-Dimensional Ferroelectric α-In ₂ Se ₃ : Implications for Ferroelectric Optoelectronic Devices

As a prototypical two-dimensional ferroelectric semiconductor with atomic-scale thickness, high carrier mobility, and strong light–matter interaction, α-In 2 Se 3 has attracted significant attention for next-generation nanoscale optoelectronic devices. However, its intrinsic functional tunability remains limited. In this work, based on first-principles calculations, we systematically investigate the effect of vacancy engineering on the electronic structure, optical properties, and photocurrent response of monolayer α-In 2 Se 3 . The results show that In vacancies convert α-In 2 Se 3 from a nonmagnetic semiconductor to a magnetic semiconductor with spin-split electronic states, whereas Se vacancies induce a tunable semiconductor-to-metal transition during ferroelectric polarization switching. Moreover, vacancy-induced defect states significantly extend the optical absorption edge from the visible to the near- and mid-infrared region, enhancing infrared photoresponse. Notably, the spin-split defect states near the Fermi level in In-vacancy systems enable spin-selective optical transitions, generating highly spin-polarized photocurrents. Overall, vacancy engineering enables dual responses in monolayer α-In 2 Se 3 spin-polarized photocurrent and switchable ferroelectric polarization─providing an effective strategy to modulate electronic, optical, and spin-optoelectronic properties and offering opportunities for the design of ferroelectric photodetectors, spin-optoelectronic devices, and multifunctional nanoscale electronic systems.