Prediction of Group-IV Multiferroic Films with Giant Mid-infrared Responsivity

Abstract

Achieving ferroelectric (FE) polarization in two-dimensional (2D) group-IV materials has been a long-sought objective, owing to their significant potential in next-generation Si-based non-volatile logic and memory devices. Here, we demonstrate that atomic rearrangements at the crystallographic planes of group-IV materials can reconstruct the local coordination environment, thereby inducing FE polarization in the resulting thin films. We identify 14 previously unreported 2D phases of group-IV films, with the (111)-derived Pmc2₁ phase exhibiting the lowest energy among all known group-IV 2D structures. Moreover, its monolayer can be readily exfoliated due to the low exfoliation energy, comparable to experimentally accessible 2D materials. These group-IV films display multiferroic ordering and diverse electronic functionalities, including low switching barriers, ultrahigh electron mobility, and strongly polarization-selective absorption and mid-wavelength infrared responsivity spanning the full 3–5 μm window. Importantly, the multiferroic transition allows interconversion among six symmetry-equivalent FE variants, offering a non-volatile approach for reconfiguring the orientation-dependent, polarization-selective optical transitions via ferroic switching. Our findings provide valuable insights into the FE mechanism in group-IV films, opening new avenues for the design and discovery of IV-based FE devices, and advancing the understanding of the rich physics in tetrahedral semiconductors.