Indium selenide ferroelectrics

In₂Se₃ (α and β′ polymorphs)

Also called α-In₂Se₃, β′-In₂Se₃, III₂–VI₃ ferroelectrics

van der Waals crystal semiconductor

A semiconductor that is also a ferroelectric, down to a single layer. In α-In₂Se₃ small shifts of atoms inside each five-atom-thick layer create an electric polarisation that points both out of and within the plane, with the two directions locked together, and an electric field can flip it. Because the material also conducts like a semiconductor with a band gap of about 1.3 eV, one flake can be a transistor channel, a memory and a photodetector at once – and its polar order persists to around 700 K.

Data sheet

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Kind of sheet: van der Waals crystal
Peels off a layered crystal, one sheet at a time
Behaves as: semiconductor
Band gap: ~1.3 eV, direct (α-In₂Se₃)

In colour: this family, 1.3 eV. In grey: the other 39 families on the catalogue’s chart, each at the middle of its range.
Thickness: Monolayer flakes measure ~1.2 nm
Structure: Se–In–Se–In–Se quintuple layers stacked by van der Waals forces, with indium in both tetrahedral and octahedral sites. α-In₂Se₃ comes in 2H and 3R stackings and lacks an inversion centre (3R: R3m); β′-In₂Se₃ carries one-dimensional superstructures within each layer
Stability: Reasonably stable under ambient conditions – photodetector studies credit a self-terminated surface without a native oxide. Transistors still benefit from atomic-layer-deposited Al₂O₃ passivation, and heating can convert one polymorph into another, so thermal budgets during processing matter.
First made: Known as a bulk compound for decades; room-temperature 2D ferroelectricity predicted in 2017 (Ding and colleagues) and observed in α-In₂Se₃ flakes the same year (Zhou and colleagues)

Compare with other materials

Key properties

α-In₂Se₃: out-of-plane and in-plane polarisation are locked together – reversing one with a vertical field rotates the other
Switchable polarisation at room temperature down to monolayer flakes about 1.2 nm thick
Polar order persists to ~700 K in atomically thin crystals, stabilised by the locking itself rather than by electrode screening
Band gap ~1.3 eV; photodetectors reach responsivities of a few hundred A W⁻¹ with millisecond response times
β′-In₂Se₃: in-plane ferroelectricity tied to one-dimensional superstructures stable to 200 °C, whose nanostripes turn out to be antiferroelectric – settling a four-decade debate over their structure
Several polymorphs and stackings – 2H and 3R α, β and β′ – so phase identification is part of every measurement

How it is made

Bulk crystals by melt or vapour growth, with conditions chosen to select the polytype
Physical vapour deposition of monolayer α-In₂Se₃ flakes, and low-temperature molecular-beam epitaxy of large-area monolayers on graphene
Mechanical exfoliation of α and β′ crystals down to a few layers

Uses, and how close they are

Ferroelectric semiconductor field-effect transistors for non-volatile memorylab
Ferroelectric Schottky diodes and 2D ferroelectric gates, including graphene FeFETslab
Sensitive, fast photodetectorslab
Artificial synapses for neuromorphic hardwarelab
Phase-change memorylab

Readiness runs lab → prototype → pilot → deployed.

Open problems

How does a ferroelectric that is also a semiconductor keep its polarisation when mobile carriers can screen it or leak – and what limits retention in transistors?
Which polymorph and stacking sits in a given device, and how do α, β and β′ phases convert during growth, processing and switching?
Can wafer-scale films be grown at back-end-of-line temperatures without losing ferroelectric switching?
Can the competing ferroelectric and antiferroelectric orders of β′-In₂Se₃ be switched on purpose?

Going deeper

Short notes for specialists. Choose a lens in the header and yours comes first.

For theoreticians · your lens

In₂Se₃ has become the model for intrinsic 2D ferroelectricity. First-principles calculations predicted room-temperature polarisation both out of and within the plane for α-In₂Se₃ and other III₂–VI₃ layers, and experiment confirmed that the two components are locked: out-of-plane dipoles are tied to an in-plane lattice asymmetry, which stabilises polarisation against the depolarising field that normally destroys it in ultrathin films. Because the material is a semiconductor, band bending and free-carrier screening enter the energetics, so switching barriers computed for a neutral slab are only a starting point. In β′-In₂Se₃, ferroelectric and antiferroelectric nanostripe orders compete within one layer – a natural test for models of 2D polar domains.

For experimentalists · your lens

Identify the phase first: 2H and 3R α-In₂Se₃, β and β′ look alike under an optical microscope but differ in Raman spectra, second-harmonic generation and electron diffraction. Piezoresponse loops alone do not prove ferroelectricity in a semiconductor with mobile charges; combine them with SHG switching or device hysteresis that tracks the polarisation. For β′ flakes, use polarised optical microscopy, since in-plane domains show strong linear dichroism. Keep processing temperatures low to avoid phase conversion.

For engineers · your lens

The attraction is a memory that is also the channel: in a ferroelectric semiconductor transistor the polarisation of α-In₂Se₃ itself stores the bit, so an ordinary amorphous gate dielectric can replace a crystalline ferroelectric insulator. Early devices combine large memory windows with high on/off ratios, and ferroelectric Schottky junctions on MBE-grown monolayers reach electroresistance ratios in the millions. Retention and endurance statistics, wafer-scale growth within thermal budgets and polymorph control across a wafer are still open.

In the research tracks

Theory frontiers

Sliding and in-plane ferroelectricity

Growth methods

Readiness assessments

2D memristors and neuromorphic devices · TRL 3

Recent news

The newest items tagged In₂Se₃, from the news feed updated 5 Oct 2026.

Preprintnot yet peer reviewed 30 Sep 2026 arXiv

Topological Hall Effect Induced by Chiral Spin Textures at the Ferroelectric/Ferromagnetic Interface

Chiral spin textures, largely driven by the Dzyaloshinskii-Moriya interaction, offer significant potential for next-generation computing technologies due to their chirality and topological stability. Ferroelectric/ferromagnetic van der Waals heterostructures are particularly appealing because they can combine…

TheoryFe₃GeTe₂, Fe₃GaTe₂ In₂Se₃

Preprintnot yet peer reviewed 16 Sep 2026 arXiv

Fractional-Quantum Ferroelectrics: A Route to High-Mobility Ferroelectric Semiconductors

Ferroelectric semiconductors are promising for multifunctional electronics, yet their typically low carrier mobilities remain a major limitation. Using first-principles phonon-limited transport calculations for monolayer In₂Se₃, we show that this limitation depends critically on the microscopic origin of…

TheoryIn₂Se₃

Preprintnot yet peer reviewed 10 Sep 2026 arXiv

Interplay of spin-lattice and electronic coupling far above Neel ordering in 2D antiferromagnetic CrPS4 and its interface manifestation

A short-range spin correlation driven, strongly intercoupled spin-phonon-electronic state far above TN (~38K) is identified in the low dimensional van der Waals antiferromagnet CrPS4. Temperature-dependent Raman spectroscopy reveals spin-phonon coupling persisting up to T*~120K, concomitant with local lattice…

ExperimentTheoryIn₂Se₃ CrPS₄

Preprintnot yet peer reviewed 30 Jun 2026 arXiv

Fully compensated ferrimagnetic triferroics and multistate transport in hidden-phase wurtzite MnSe monolayer

Fully compensated ferrimagnets (fFIMs) have attracted interest due to their compensated moments and nonrelativistic spin splitting across the Brillouin zone. Known fFIMs, however, are mostly restricted to complex three-dimensional (3D) systems or require external fields in two-dimensional (2D) heterostructures, leaving…

ExperimentTheoryIn₂Se₃