Emergence of ferroelectricity in a nonferroelectric monolayer

Abstract

Ferroelectricity in ultrathin two-dimensional (2D) materials has attracted broad interest due to potential applications in nonvolatile memory, nanoelectronics and optoelectronics. However, ferroelectricity is barely explored in materials with native centro or mirror symmetry, especially in the 2D limit. Here, we report the first experimental realization of room-temperature ferroelectricity in van der Waals layered GaSe down to monolayer with mirror symmetric structures, which exhibits strong intercorrelated out-of-plane and in-plane electric polarization. The origin of ferroelectricity in GaSe comes from intralayer sliding of the Se atomic sublayers, which breaks the local structural mirror symmetry and forms dipole moment alignment. Ferroelectric switching is demonstrated in nano devices fabricated with GaSe nanoflakes, which exhibit exotic nonvolatile memory behavior with a high channel current on/off ratio. Our work reveals that intralayer sliding is a new approach to generate ferroelectricity within mirror symmetric monolayer, and offers great opportunity for novel nonvolatile memory devices and optoelectronics applications.

Tunable non-volatile memories based on 2D InSe/h-BN/GaSe heterostructures towards potential multifunctionality

“…Therefore, it is deducted that InSe is the γ -phase 22,32 and GaSe may be the ε -phase. 33,34 However, it is worth mentioning that from Raman analysis alone cannot exclusively rule out the existence of γ -phase 14 or 2H -phase 22 GaSe. In the Raman spectrum of the InSe/ h -BN/GaSe heterostructure (Fig.…”

“…The 2D layered GaSe generally shows p -type semiconductor characteristics with a direct bandgap of ∼2 eV and high photoresponsivity with direct-to-indirect bandgap transition. 13 Along with the intralayer sliding induced ferroelectricity 14 of GaSe, it indicates a promising multifunctionality of additional optoelectric, ferromagnetic manipulation in InSe/GaSe related heterostructures for future device downscaling and energy consumption reduction.…”

“…The 2D layered GaSe generally shows p-type semiconductor characteristics with a direct bandgap of ∼2 eV and high photoresponsivity with direct-to-indirect bandgap transition. 13 Along with the intralayer sliding induced ferroelectricity 14 of GaSe, it indicates a promising multifunctionality of additional optoelectric, ferromagnetic manipulation in InSe/GaSe related heterostructures for future device downscaling and energy consumption reduction. Therefore, there are many studies based on van der Waals heterostructures such as InSe/h-BN/graphene memories, 15 GaSe memtransistors, 16 black phosphorus (BP)/Al 2 O 3 memory devices, 17 and WSe 2 /h-BN/graphene non-volatile programmable p-n junction devices, 18 but with limited device functionality (Table 1).…”

Ultra-High-Density Ferroelectric Array Formed by Sliding Ferroelectric Moiré Superlattices

“…Ferroelectric memory devices with fast-switching speed and ultrahigh density are considered promising candidates to meet the massive data storage demands in the post-Moore era. In particular, ferroelectric memories based on 2D materials have garnered increasing research interest in recent years due to their unique properties, which are unattainable in conventional materials. , Especially noteworthy are those with out-of-plane (OOP) ferroelectric polarization at above room temperature, such as CuInP 2 S 6 and In 2 Se 3 , since OOP polarization is technologically easier to manipulate. − However, intrinsic 2D van der Waals (vdW) ferroelectrics are rather rare due to the strict constraints of the surface depolarization field . The discovery of sliding ferroelectricity with OOP polarization in 2D vdW materials, through the specific stacking sequences and easy sliding between atomic layers, challenges the conventional understanding of ferroelectric behavior and reveals a vast collection of new 2D ferroelectrics. − This phenomenon has been experimentally demonstrated in bilayers of nonferroelectric BN − and transition metal dichalcogenides, − such as WTe 2 and MoS 2 .…”

“…In particular, ferroelectric memories based on 2D materials have garnered increasing research interest in recent years due to their unique properties, which are unattainable in conventional materials. 1,2 Especially noteworthy are those with out-ofplane (OOP) ferroelectric polarization at above room temperature, such as CuInP 2 S 6 3 and In 2 Se 3 , 4 since OOP polarization is technologically easier to manipulate. 5−8 However, intrinsic 2D van der Waals (vdW) ferroelectrics are rather rare due to the strict constraints of the surface depolarization field.…”