Tuning Structural, Electronic, and Optical Properties of α-In ₂ Se ₃ by an External Electric Field

The various polymorphic structures of ferroelectric semiconductors contribute to distinct electronic properties. Fully researching the mechanisms of phase transitions and controlling these phases through external stimuli offers a promising route to tailor the material’s optoelectronic behaviors and provides ideas for the development of functional devices. In this paper, the phase transition of In 2 Se 3 and related optoelectronic properties under the condition of an electric field are investigated systematically, from two complementary aspects: the field-driven structural transition mechanism in the bulk and the optical response modulation in monolayer systems relevant to two-dimensional device scales. The results show that applying an in-plane electric field of 0.05–0.20 V Å –1 rearranges the Se-4 p orbitals and promotes electron transitions, inducing the migration of Se 2– ions as well as interlayer sliding and the progressive evolution of the local coordination environment, thereby triggering the transformation from the α phase to the β phase in In 2 Se 3 . This field-induced α–β phase transition reveals the strong coupling between lattice polarization and electronic structure in In 2 Se 3, providing microscopic insight into the interplay between electric-field control and structural stability in ferroelectric layered materials. Building on this mechanism, we further quantify in monolayer α-In 2 Se 3 how the electric field modulates the band-edge positions and the linear optical response. Furthermore, second-harmonic generation measurements reveal exceptionally large nonlinear coefficients, with the out-of-plane d 33 exceeding 10 3 pm V –1, confirming their strong potential for infrared-to-visible frequency conversion. This work clarifies the microscopic mechanism of electric-field-driven phase transitions in In 2 Se 3, demonstrating a practical route for tuning its electronic and optical responses as well as providing a basis for the design of phase-change optoelectronic devices.