Effect Of Vertical Strain Research Articles

Functional groups and vertical strain regulate the electronic properties of Nb2NT2/MoTe2 heterojunction

In the current effort, a novel attempt to construct heterojunctions using Nb2N two-dimensional MXene materials with fascinating property and MoTe2 transition metal disulfide compounds is proposed. The effect of vertical strain on the electronic structure and interfacial contact properties of the heterojunction is investigated by first principles calculations. The O, F, and OH functional groups prefer to be adsorbed on top of the N atoms of the Nb2N MXene material. The configuration III of heterojunction has the lowest energy and stable model, and the equilibrium layer spacing is within the range of 3.061 Å to 3.328 Å, indicating that they belong to typical vdW heterojunctions. The large work function difference between the two components induces the transfer and rearrangement of charge. 0.12 e per cell spontaneously transfer from MoTe2 to Nb2NO2 layer. In contrast, the Nb2NF2 and Nb2N(OH)2 layers transfer 0.01 e and 0.21 e to the MoTe2 layer, respectively. n-type Ohmic contacts are formed in O terminal system, while p-type and n-type Schottky contacts are formed in F and OH terminal systems, respectively. Additionally, for vertical strain, with the decrease of the layer spacing, the p-type Schottky barrier height (SBH) decreases from 0.270 eV to 0.095 eV in former system, meanwhile the n-type Schottky barrier height in the latter system also decreases from 0.260 eV to 0.156 eV. These regulations of interest lays a theoretical foundation for bandgap engineering and Schottky junction preparation and opens a window into MXene-based heterojunction electron device.

First-principles calculations to investigate electronic properties of ZnO/PtSSe van der Waals heterostructure: Effects of vertical strain and electric field

In the present study, we report the electronic properties of ZnO/PtSSe van der Waals heterostructure by using the density functional theory. Two different stacking configurations ZnO/SePtS and ZnO/SPtSe are formed with very small lattice mismatch and they are confirmed to be stable through ab initio molecular dynamic simulations. Obtained results demonstrate that both ZnO/SePtS and ZnO/SPtSe stacking configurations are indirect semiconductors. At the ground state, band gaps of ZnO/SePtS and ZnO/SPtSe configurations are respectively 0.895 and 0.448 eV, that quite smaller than that of both ZnO and PtSSe monolayers. The band gap of heterostructure depends strongly on the interlayer distance and electric field. Our findings not only give insight into the physical properties of heterostructures but also open up possibilities for their application in electronic devices.

Effects of vertical strain and electric field on the electronic properties and interface contact of graphene/InP vdW heterostructure

The graphene/InP Schottky heterojunction solar cells, possessing a great significance in special applications of space optoelectronic devices, have been realized experimentally, however, the mechanism of the contact nature is lack. In this contribution, using first-principles calculation, we investigate the electronic properties and interface contacts of heterostructures through varying interlayer spacing and applying external electric fields. Our results indicate that graphene/InP is a typical vdW heterostructure with an equilibrium layer spacing of 3.65 Å. A small band gap of approximately 67 meV is opened, indicating a promising prospect concerning optoelectronic devices. Meanwhile, the formation of built-in electric field significantly promotes the separation of photogenerated electron-hole pairs. Additionally, the p-type Schottky contact with 0.04 eV p-type and 2.03 eV n-type SBH, respectively, is formed in the most stable configuration. Importantly, when the interlayer distance decreases below 3.6 Å, the heterostructure changes from p-type Schottky contact to p-type Ohmic contact. When exerting a negative electric field, the heterostructure belongs to p-type Ohmic contact. As the electric field increases to 0.55 V/Å, the transition from p-type to n-type Schottky contact is observed. These findings may be expected to have significant guiding value for design and fabrication of nano-devices based on graphene/InP vdW heterostructure.

Effects of vertical strain and electrical field on electronic properties and Schottky contact of graphene/MoSe2 heterojunction

Fabricating a low Schottky barrier is still a great challenge in electrical transport behavior of nano field effect transistors (FETs). To settle this problem, the electronic properties and Schottky contact of the graphene/MoSe2 heterojunction employing various vertical strains and external electrical fields are investigated with density functional theory (DFT) to obtain low Schottky barrier. Our calculation illustrates that in the graphene/MoSe2 heterojunction, the intrinsic electronic properties of components are well preserved owing to the weak van der Waals (vdW) mutual interaction between graphene and MoSe2 monolayer. Furthermore, there is an n-type Schottky contact formed with an n-type Schottky barrier height (SBH) of 0.56 eV at the interface of graphene/MoSe2 heterojunction. It is worth noting that the type and the height of Schottky barrier are susceptible to the external electrical field or strain employed perpendicularly to the graphene/MoSe2 heterojunction. And the SBH of the interface can be reduced by tuning the interlayer distance (d) or the electrical field intensity (E). Moreover, Schottky contact transforms from n-type to p-type at d = 3.22 Å or E = +0.08 V/Å. Additionally, the Ohmic contact occurs when the magnitude of positive or negative electrical field is larger than 0.40 V/Å, respectively. Additionally, the heterojunction maintaining high carrier mobility is inferred from the effective masses of electron and hole, namely, 0.074 m0 and 0.055 m0, respectively. Our study may put forward effective strategies to enhance the electronic performance of MoSe2-based vdW heterojunction FETs.

Type II GaS/AlN van der Waals heterostructure: Vertical strain, in-plane biaxial strain and electric field effect

In this work, the geometrical structure, stability, electronic and optical properties of the GaS/AlN van der Waals heterostructure have been explored based on first principles calculations considering the effect of vertical strain, in-plane biaxial strain and the electric field. It is demonstrated that, the GaS/AlN van der Waals heterostructure possesses an intrinsic typical type-II band alignment with an indirect band gap of 1.65 eV. Due to the difference of work functions between monolayer GaS and AlN, the electrons transfer from AlN layer to GaS layer, causing a build-in electric field which facilitates the separation of free electrons and holes. The band gap value of the heterostructure is insensitive to the vertical strain, while in-plain biaxial strain is an effective way to tune the band gap. The band gap value is in the range of 0.68–1.82 eV under in-plane biaxial strain of −5%–5%. The band offsets of the heterostructure can be increased by positive electric field and decreased by negative electric field. Meanwhile, the type-II band alignment of the heterostructure is retained under vertical strain, in-plane biaxial strain and the electric field. In addition, for the heterostructure, compare to constituent layers, the optical absorption is enhanced in visible region. These results render GaS/AlN heterostructure as a good candidate for photovoltaic devices. • GaS/AlN van der Waals heterostructure possesses a typical type-II band alignment with an indirect band gap of 1.65 eV. • The band gap of the heterostructure can be effectively tuned by strains and electric field. • The type-II band alignment of the heterostructure is retained under strains and electric field. • Compare to constituent layers, the optical absorption coefficient of the heterostructure is enhanced in visible region.

Layered graphene/GaS van der Waals heterostructure: Controlling the electronic properties and Schottky barrier by vertical strain

In this work, we construct an ultrathin graphene/GaS heterostructure and investigate its electronic properties as well as the effect of vertical strain using density functional theory. The calculated results of the equilibrium interlayer spacing (3.356 Å) and the binding energy show that the intrinsic properties of isolated graphene and GaS monolayers can be preserved and the weak van der Waals interactions are dominated in the heterostructures. The van der Waals heterostructure (vdWH) forms an n-type Schottky contact with a small Schottky barrier height of 0.51 eV. This small Schottky barrier height can also be tuned by applying vertical strain. Furthermore, we find that the n-type Schottky contact of the vdWH can be changed to p-type when the interlayer spacing is decreased and exceeded to 2.60 Å. These findings show the great potential application of the graphene/GaS vdWH for designing next generation devices.

Effects of vertical strain on zigzag graphene nanoribbon with a topological line defect

We report the elastic, electronic and magnetic properties of naked ZGNRs with topological line defects (LD-ZGNRs) lying symmetrically on the ribbon's middle under vertical strains at four types of line defect atoms by using a first-principles approach. By changing the position and size of the local deformation of the ribbon, the optimal position is obtained. Moreover, an apparent spin-splitting of the energy band is obtained when a local deformation is created by the vertically applied strain.