Emerging van der Waals ferroelectrics: Unique properties and novel devices

Abstract

The past few decades have witnessed extensive and intensive studies on ferroelectric materials with switchable electric polarization due to their broad device applications. Emerging van der Waals (vdW) layered ferroelectrics ingeniously assemble strong covalent-bonded polar or non-polar monolayers through weak vdW forces. These atom arrangements contrast with the stacking of conventional oxide ferroelectrics, enabling unprecedented ferroelectric physics in terms of polarization origin, polar stabilization, and switching kinetics. Combined with other inherent optical and electrical features, the vdW ferroelectrics can undoubtedly provide a new, versatile platform for advancing fundamental physics and revolutionizing device technology. In this review, we summarize the unique ferroelectric properties in experimentally confirmed vdW ferroelectrics, particularly those properties that expand our understanding of ferroelectric switching. We also elucidate how some of these properties can intrinsically reduce depolarized instability at the atomic limit. Finally, we discuss innovative devices enabled by distinct properties of vdW ferroelectrics for electronic, optoelectronic, and energy harvesting applications, and highlight possible future research lines.

Electrostatic Coupling in MoS2/CuInP2S6 Ferroelectric vdW Heterostructures

“…thus attracting increasing attention in recent years. [1][2][3][4][5][6] The spontaneous polarization of the ferroelectrics could serve as an electrostatic knob to actively tune the carrier concentrations of the 2D semiconductors and consequently, their electronic transport, luminescent, and optoelectronic properties. [7][8][9][10][11][12][13] As a predominant interface effect, the electrostatic coupling pivots on the quality of the vdW interface between the ferroelectric and the semiconductor.…”

Gigantic photostriction effect in monolayer semiconductors

“…Similarly, the Raman peak of 3L WSe2 at 20 cm -1 , corresponding to interlayer in-plane shear mode, is observed at 16 cm -1 in 2L and absent in monolayer. 𝐴 𝑔 1 and 𝐴 1𝑔 2 are the first and second-order out-of-plane vibrations between chalcogen atoms, and 𝐸 2𝑔 1 is the first-order in-plane vibration between the transition metal and chalcogen atoms. Since 𝐴 𝑔 1 mode is independent of the incident power, we focus on the 𝐸 2𝑔 1 mode to investigate the photostriction effect.…”

Indium Selenide (In2Se3) – An Emerging Van‐der‐Waals Material for Photodetection and Non‐Volatile Memory Applications

“…[61] Finally, the coexistence of OOP and IP polarizations was revealed in the bilayer and monolayer (~1.2 nm) form of hexagonal (2H) α-In 2 Se 3 nanoflake using PFM, as reported by Xue et al [62] The layered α-phase In 2 Se 3 possesses two polymorphs (2H and 3R), and both of them exhibit IP and OOP ferroelectricity at room-temperature. [63,64] Furthermore, few reports claimed that β-In 2 Se 3 also exhibits ferroelectric behaviour even though it is structurally centrosymmetric. For example, in 2018, Zheng et al demonstrated room-temperature IP ferroelectricity in 45 nm thick β-In 2 Se 3 .…”