Two-Dimensional Ferroelectric Ga2O3 Bilayers with Unusual Strain-Engineered Interlayer Interactions

Two-dimensional (2D) van der Waals (vdW)materials and their bilayers have stimulated enormous interests infundamental research and technological applications. Recently, agroup of 2D vdW III2-VI3materials with out-of-plane ferroelec-tricity have attracted substantial attention. In this work, thestructural, electronic, and optical properties of a 2D ferroelectricGa2O3bilayer system are systematically studied using anab initiocomputational method. Intrinsic dipoles of the two free-standingmonolayers lead to three distinct dipole models (one ferroelectricand two antiferroelectric models). The stable stacking config-urations of ferroelectric and antiferroelectric dipole models can betransferred with a polarization reversal transition of the monolayerswithout an additional operation. Interlayer perturbation effectscombined with biaxial-strain engineering lead to high tunablility ofthe electronic and optical properties of the bilayer systems. Surprisingly, the results reveal a phase transition from a vdW to ionicinterlayer interaction induced by in-plane biaxial tensile strain. Detailed analyses suggest a transition mechanism based on the ionicbonding nature of the Ga2O3system, involving interlayer rearrangement of anions to compensate the symmetry breaking of theheavily distorted ionic folding configurations. These insights can open new prospects for future experimental synthesis,characterization, and application of 2D Ga2O3atomically thin layered systems.