Achieving Ferroelectricity in a Centrosymmetric High-Performance Semiconductor by Strain Engineering

Phase engineering by strain in 2D semiconductors is of great importance for a variety of applications. Here, a study of the strain-induced ferroelectric (FE) transition in bismuth oxyselenide (Bi₂O₂Se) films, a high-performance (HP) semiconductor for next-generation electronics, is presented. Bi₂O₂Se is not FE at ambient pressure. At a loading force of ≳400 nN, the piezoelectric force responses exhibit butterfly loops in magnitude and 180° phase switching. By carefully ruling out extrinsic factors, these features are attributed to a transition to the FE phase. The transition is further supported by the appearance of a sharp peak in optical second-harmonic generation under uniaxial strain. In general, solids with paraelectrics at ambient pressure and FE under strain are rare. The FE transition is discussed using first-principles calculations and theoretical simulations. The switching of FE polarization acts as a knob for Schottky barrier engineering at contacts and serves as the basis for a memristor with a huge on/off current ratio of 10⁶. This work adds a new degree of freedom to HP electronic/optoelectronic semiconductors, and the integration of FE and HP semiconductivity paves the way for many exciting functionalities, including HP neuromorphic computing and bulk piezophotovoltaics.