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Prediction of intrinsic two-dimensional ferroelectrics in In 2 Se 3 and other III 2 -VI 3 van der Waals materials

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ABSTRACT

Interest in two-dimensional (2D) van der Waals materials has grown rapidly across multiple scientific and engineering disciplines in recent years. However, ferroelectricity, the presence of a spontaneous electric polarization, which is important in many practical applications, has rarely been reported in such materials so far. Here we employ first-principles calculations to discover a branch of the 2D materials family, based on In2Se3 and other III2-VI3 van der Waals materials, that exhibits room-temperature ferroelectricity with reversible spontaneous electric polarization in both out-of-plane and in-plane orientations. The device potential of these 2D ferroelectric materials is further demonstrated using the examples of van der Waals heterostructures of In2Se3/graphene, exhibiting a tunable Schottky barrier, and In2Se3/WSe2, showing a significant band gap reduction in the combined system. These findings promise to substantially broaden the tunability of van der Waals heterostructures for a wide range of applications.

No MeSH data available.


Electronic structures of In2Se3-based heterostructures.(a) Electronic band structure of one quintuple layer (QL) ferroelectric In2Se3 in the FE-ZB′ phase (calculated by HSE06); here the inset shows the first Brillouin zone with the high symmetric points of Γ, Μ and ϰ indicated. (b–e) Demonstration of a tunable Schottky barrier at the interface of a one QL FE-ZB′ In2Se3/graphene heterostructure. (b,d) The side views of the heterostructure. The corresponding electronic band structures are shown in c,e (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the graphene layer are highlighted in red and yellow, respectively. The green circles indicate the Dirac points of the graphene layer. (f–i) Demonstration of a significant band gap reduction in a one QL FE-ZB′ In2Se3/WSe2 heterostructure. (f,h) The side views of the heterostructure with the electric dipole of the In2Se3 layer pointing downwards and upwards, respectively. The corresponding electronic band structures are shown in g,i (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the WSe2 layer are highlighted in red and blue, respectively. The Fermi level of each system is shifted to energy zero in all the band structure plots.
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f5: Electronic structures of In2Se3-based heterostructures.(a) Electronic band structure of one quintuple layer (QL) ferroelectric In2Se3 in the FE-ZB′ phase (calculated by HSE06); here the inset shows the first Brillouin zone with the high symmetric points of Γ, Μ and ϰ indicated. (b–e) Demonstration of a tunable Schottky barrier at the interface of a one QL FE-ZB′ In2Se3/graphene heterostructure. (b,d) The side views of the heterostructure. The corresponding electronic band structures are shown in c,e (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the graphene layer are highlighted in red and yellow, respectively. The green circles indicate the Dirac points of the graphene layer. (f–i) Demonstration of a significant band gap reduction in a one QL FE-ZB′ In2Se3/WSe2 heterostructure. (f,h) The side views of the heterostructure with the electric dipole of the In2Se3 layer pointing downwards and upwards, respectively. The corresponding electronic band structures are shown in g,i (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the WSe2 layer are highlighted in red and blue, respectively. The Fermi level of each system is shifted to energy zero in all the band structure plots.

Mentions: Next, we demonstrate the device potential of the discovered 2D ferroelectric materials in van der Waals heterostructures, focusing on the electrical transport properties. As a reference, a single ferroelectric In2Se3 QL is a semiconductor with an indirect band gap of 1.46 eV (calculated by HSE06, 0.78 eV by GGA-PBE) (Fig. 5a). Owing to the presence of the out-of-plane electric polarization of the ferroelectric layer, there is a built-in electric field within the material, leading to different alignments of the energy bands with respect to the vacuum level on different sides of a given ferroelectric QL. For a ferroelectric In2Se3 QL, such a difference is as large as 1.37 eV (calculated by HSE06). As a van der Waals 2D material is stacked with a ferroelectric In2Se3 layer, the energy bands of the two components are approximately aligned with respect to the vacuum level, due to their weak van der Waals interaction. Therefore, as different sides of the ferroelectric layer are in contact with the other 2D material, different band alignments result in different global electronic structures. As the first specific system, we consider a bilayer heterostructure by stacking a QL of ferroelectric In2Se3 onto a single-layer graphene, which is a non-ferroelectric semimetal. As shown in Fig. 5b–e, the Schottky barrier across the interface can be altered by switching the electric dipole orientation of the In2Se3 layer. The magnitude of the electric dipoles of the system is 0.11 and 0.03 eÅ per In2Se3 unit cell for the two oppositely polarized configurations as shown in Fig. 5b,d, respectively. The next bilayer heterostructure system considered is formed by stacking a QL of ferroelectric In2Se3 on a monolayer of WSe2, which is a non-ferroelectric semiconductor. As shown in Fig. 5f–i, the band shift leads to a significant band gap reduction when switching the electric dipole orientation of the In2Se3 layer. The magnitude of the electric dipoles of the system is 0.10 and 0.06 eÅ per In2Se3 unit cell for the two oppositely polarized configurations as shown in Fig. 5f,h, respectively. For both heterostructures, the reduction of the electric dipoles in one of the polarized configurations can be attributed to the screening effects due to the charge transfer between the two layers as indicated in Fig. 5e,i. The influence of the graphene and WSe2 layers on the energetics and kinetics of the polarization reversal processes of the ferroelectric In2Se3 layer is discussed in Supplementary Note 3. The observed tunable band alignments with the ferroelectric layer can be exploited for different technological applications, such as for non-volatile memory devices or in graphene-based electronics. It is particularly worthwhile to note that the tunability in the properties can be achieved by the application of an external field, but the desired functionalities can be preserved even after the external field is removed. To provide a generic guideline for the design of desirable heterostructures, a schematic diagram of the band alignments of a single ferroelectric In2Se3 QL is provided in Supplementary Fig. 13.


Prediction of intrinsic two-dimensional ferroelectrics in In 2 Se 3 and other III 2 -VI 3 van der Waals materials
Electronic structures of In2Se3-based heterostructures.(a) Electronic band structure of one quintuple layer (QL) ferroelectric In2Se3 in the FE-ZB′ phase (calculated by HSE06); here the inset shows the first Brillouin zone with the high symmetric points of Γ, Μ and ϰ indicated. (b–e) Demonstration of a tunable Schottky barrier at the interface of a one QL FE-ZB′ In2Se3/graphene heterostructure. (b,d) The side views of the heterostructure. The corresponding electronic band structures are shown in c,e (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the graphene layer are highlighted in red and yellow, respectively. The green circles indicate the Dirac points of the graphene layer. (f–i) Demonstration of a significant band gap reduction in a one QL FE-ZB′ In2Se3/WSe2 heterostructure. (f,h) The side views of the heterostructure with the electric dipole of the In2Se3 layer pointing downwards and upwards, respectively. The corresponding electronic band structures are shown in g,i (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the WSe2 layer are highlighted in red and blue, respectively. The Fermi level of each system is shifted to energy zero in all the band structure plots.
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f5: Electronic structures of In2Se3-based heterostructures.(a) Electronic band structure of one quintuple layer (QL) ferroelectric In2Se3 in the FE-ZB′ phase (calculated by HSE06); here the inset shows the first Brillouin zone with the high symmetric points of Γ, Μ and ϰ indicated. (b–e) Demonstration of a tunable Schottky barrier at the interface of a one QL FE-ZB′ In2Se3/graphene heterostructure. (b,d) The side views of the heterostructure. The corresponding electronic band structures are shown in c,e (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the graphene layer are highlighted in red and yellow, respectively. The green circles indicate the Dirac points of the graphene layer. (f–i) Demonstration of a significant band gap reduction in a one QL FE-ZB′ In2Se3/WSe2 heterostructure. (f,h) The side views of the heterostructure with the electric dipole of the In2Se3 layer pointing downwards and upwards, respectively. The corresponding electronic band structures are shown in g,i (calculated by GGA-PBE). The bands derived from the In2Se3 layer and the WSe2 layer are highlighted in red and blue, respectively. The Fermi level of each system is shifted to energy zero in all the band structure plots.
Mentions: Next, we demonstrate the device potential of the discovered 2D ferroelectric materials in van der Waals heterostructures, focusing on the electrical transport properties. As a reference, a single ferroelectric In2Se3 QL is a semiconductor with an indirect band gap of 1.46 eV (calculated by HSE06, 0.78 eV by GGA-PBE) (Fig. 5a). Owing to the presence of the out-of-plane electric polarization of the ferroelectric layer, there is a built-in electric field within the material, leading to different alignments of the energy bands with respect to the vacuum level on different sides of a given ferroelectric QL. For a ferroelectric In2Se3 QL, such a difference is as large as 1.37 eV (calculated by HSE06). As a van der Waals 2D material is stacked with a ferroelectric In2Se3 layer, the energy bands of the two components are approximately aligned with respect to the vacuum level, due to their weak van der Waals interaction. Therefore, as different sides of the ferroelectric layer are in contact with the other 2D material, different band alignments result in different global electronic structures. As the first specific system, we consider a bilayer heterostructure by stacking a QL of ferroelectric In2Se3 onto a single-layer graphene, which is a non-ferroelectric semimetal. As shown in Fig. 5b–e, the Schottky barrier across the interface can be altered by switching the electric dipole orientation of the In2Se3 layer. The magnitude of the electric dipoles of the system is 0.11 and 0.03 eÅ per In2Se3 unit cell for the two oppositely polarized configurations as shown in Fig. 5b,d, respectively. The next bilayer heterostructure system considered is formed by stacking a QL of ferroelectric In2Se3 on a monolayer of WSe2, which is a non-ferroelectric semiconductor. As shown in Fig. 5f–i, the band shift leads to a significant band gap reduction when switching the electric dipole orientation of the In2Se3 layer. The magnitude of the electric dipoles of the system is 0.10 and 0.06 eÅ per In2Se3 unit cell for the two oppositely polarized configurations as shown in Fig. 5f,h, respectively. For both heterostructures, the reduction of the electric dipoles in one of the polarized configurations can be attributed to the screening effects due to the charge transfer between the two layers as indicated in Fig. 5e,i. The influence of the graphene and WSe2 layers on the energetics and kinetics of the polarization reversal processes of the ferroelectric In2Se3 layer is discussed in Supplementary Note 3. The observed tunable band alignments with the ferroelectric layer can be exploited for different technological applications, such as for non-volatile memory devices or in graphene-based electronics. It is particularly worthwhile to note that the tunability in the properties can be achieved by the application of an external field, but the desired functionalities can be preserved even after the external field is removed. To provide a generic guideline for the design of desirable heterostructures, a schematic diagram of the band alignments of a single ferroelectric In2Se3 QL is provided in Supplementary Fig. 13.

View Article: PubMed Central - PubMed

ABSTRACT

Interest in two-dimensional (2D) van der Waals materials has grown rapidly across multiple scientific and engineering disciplines in recent years. However, ferroelectricity, the presence of a spontaneous electric polarization, which is important in many practical applications, has rarely been reported in such materials so far. Here we employ first-principles calculations to discover a branch of the 2D materials family, based on In2Se3 and other III2-VI3 van der Waals materials, that exhibits room-temperature ferroelectricity with reversible spontaneous electric polarization in both out-of-plane and in-plane orientations. The device potential of these 2D ferroelectric materials is further demonstrated using the examples of van der Waals heterostructures of In2Se3/graphene, exhibiting a tunable Schottky barrier, and In2Se3/WSe2, showing a significant band gap reduction in the combined system. These findings promise to substantially broaden the tunability of van der Waals heterostructures for a wide range of applications.

No MeSH data available.