Ferroelectric van der Waals heterostructures of CuInP₂S₆for non-volatile memory device applications

Two-dimensional (2D) ferroelectric materials are providing promising platforms for creating future nano- and opto-electronics. Here we propose new hybrid van der Waals heterostructures, in which the 2D ferroelectric material CuInP₂S₆(CIPS) is layered on a 2D semiconductor for near-infrared (NIR) memory device applications. Using density functional theory, we show that the band gap of the hybrid bilayers formed with CIPS can be tuned and that the optical and electronic properties can be successfully modulated via ferroelectric switching. Of the 3712 heterostructures considered, we identified 19 structures that have a type II band alignment and commensurate lattice matches. Of this set, both the CuInP₂S₆/PbSe and CuInP₂S₆/Ge₂H₂heterostructures possess absorption peaks in the NIR region that change position and intensity with switching polarisation, making them suitable for NIR memory devices. The CuInP₂S₆/ISSb, CuInP₂S₆/ISbSe, CuInP₂S₆/ClSbSe and CuInP₂S₆/ZnI₂heterostructures had band gaps which can be switched from direct to indirect with changing the polarisation of CIPS making them suitable for optoelectronics and sensors. The heterostructures formed with CIPS are exciting candidates for stable ferroelectric devices, opening a pathway for tuning the band alignment of van der Waal heterostructures and the creation of modern memory applications that use less energy.