An ab initio study of the electronic properties of the ferroelectric heterostructure In2Se3/Bi2Se3
Graphical abstract
Introduction
The increasing progress of nanotechnology in recent years has motivated the scientific community to study materials with improved or even new properties, including two-dimensional (2D) materials [1], [2], [3], [4], [5], [6], [7]. The latter, in the form of nanometric objects, have already demonstrated their effectiveness as active elements in various devices capable to meet the current needs. In particular, 2D piezoelectricity and 2D ferroelectricity [8], [9], [10] have attracted tremendous attention due to their large potential for device applications. These properties are exploited for applications as nonvolatile ferroelectric memories [11], capacitors [12], actuators [13], and sensors [14].
The ability to combine and stack 2D layers has created a new class of materials known as van der Waals heterostructures and has opened the way to design new architectures. This area has already proven to be fruitful for new properties and various functionalities, different from those of their individual 2D materials and thus created the basis for a variety of devices [15], [16]. For instance, Zhang et al. [17] have demonstrated that the photoresponsivity of a photodetector based on graphene/MoS2 heterostructures is improved by a factor of nine in comparison with a standalone graphene layer. Also, enriching the functionalities of 2D heterostructures with ferroelectric properties would open up new opportunities for their applications [18], [19], [20].
Obviously the properties of this type of heterostructures are directly linked to the properties of their elementary constituents. Recently, both experiment and theoretical studies [21], [22], [23] on In2Se3 proved that the phase presents ferroelectric properties with in- and out-of plane polarization, contrary to the phase which is not ferroelectric. This discovery puts -In2Se3 under the light to be a useful candidate to form 2D ferroelectric heterostructures with out of plane polarization [24], [25]. For example, theoretical studies [23], [26] demonstrated that the In2Se3/graphene heterostructure exhibits a Schottky barrier which can be controlled by the direction of the out-of plane intrinsic dipole of -In2Se3. Moreover, a photodetector with outstanding properties, including a photocurrent on/off ratio of 1.24 × 105 at room temperature and a maximum photoresponsivity of 26 mAW−1 at 650 nm, based on WSe2/-In2Se3 was fabricated recently [27]. On the other hand, the topological insulator Bi2Se3 [28], [29], [30], [31] is a good material to form van der Waals heterostructures with various promising applications: for instance, a high performance photodetector based on SnTe/Bi2Se3 was fabricated which exhibits remarkable properties as a high light responsivity of 145.74 mAW−1 and a maximum detectivity of 1.15 × 1010 Jones [32]. At the limit of the single layer, Bi2Se3 possesses also great carrier mobilities of electrons and holes which can reach 1.96 × 105 and 3.4 × 104 cm2 V−1 s−1, respectively, together with a high optical absorption in the near ultraviolet and visible light regions [33]. In addition, Somilkumar et al. [34] have used molecular beam epitaxy (MBE) to grow Bi2Se3/In2Se3 bilayers on Si(1 1 1) and they found that In2Se3 is suitable for the subsequent high-quality heteroepitaxy of Bi2Se3. However, to our knowledge, no theoretical work has studied the electronic properties of the In2Se3/Bi2Se3 heterostructure and more specifically their band offsets.
In this work, DFT calculations were performed to investigate the electronic properties of the ferroelectric -In2Se3/Bi2Se3 and the non-ferroelectric -In2Se3/Bi2Se3 heterostructures. Moreover, we also have investigated their band offsets under electrical field which are important quantities for material and device designs.
Section snippets
Computational details
Our first principles calculations based on density functional theory were performed using the Vienna Ab Initio Simulation Package (VASP) [35] implementing the projector augmented wave method [36]. The exchange and correlation potential was described by the Perdew-Burke-Ernzerhof functional within the generalized gradient approximation [37]. The weak van der Waals interactions are described by the dispersion correction of Tkatchenko and Scheffler [38] with iterative Hirshfeld partitioning [39]
Results and discussion
When stacking a Bi2Se3 layer on top of a -In2Se3 ferroelectric layer, two different arrangements can be obtained, noted hereafter G1 and G2, depending on the direction of the polarization vector: in the G1 configuration, the spontaneous out-of-plane electric polarization P is pointing towards Bi2Se3 while in the configuration G2 it is pointing in the other direction. The G3 configuration is constructed by stacking the Bi2Se3 layer on top of the non-ferroelectric layer -In2Se3. The different
Conclusion
In summary, the electronic properties of In2Se3/Bi2Se3 heterostructure have been investigated using density functional theory and the GW approximation. We have found that the In2Se3/Bi2Se3 ferroelectric heterostructure is a semiconductor with a direct bandgap. However, when the intrinsic polarization of In2Se3 is reversed, we have found that In2Se3/Bi2Se3 is a semiconductor with an indirect bandgap. By analysing the electron density, we found that the In2Se3/Bi2Se3 heterobilayer can be
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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