P-type Schottky Contact Research Articles

Graphene/WSeTe van der Waals heterostructure: Controllable electronic properties and Schottky barrier via interlayer coupling and electric field

The formation of the graphene-based van der Waals (vdW) heterostructures has shown great potential for designing novel electronic and optoelectronic nanodevices. Here, we construct the Graphene/WSeTe heterostructure and investigate its structural, electronic, optical and transport properties through first-principles calculations. We find that the electronic properties of both graphene and Janus WSeTe are well preserved in Graphene/WSeTe heterostructure because of the weak vdW interactions. The optical absorption of the Graphene/WSeTe heterostructure is enhanced in both regions of the visible and UV lights in comparison with that of the graphene and Janus WSeTe monolayers. The absorption coefficient of the Graphene/WSeTe heterostructure for the visible light can reach 5 × 104 cm−1, which is as twice as that of Janus WSeTe monolayer. Whereas, for the UV light, the absorption coefficient of such heterostructure can reach up to 105 cm−1. Moreover, the Graphene/WSeTe heterostructure tends to own a high carrier mobility for both electrons and holes as compared with single-layered Graphene. Especially, a band gap of about 10 meV at the Dirac cone of graphene in such heterostructures can be opened. Depending on the stacking configurations, the Graphene/WSeTe heterostructure can form the p-type Ohmic contact or p-type Schottky contact with a small Schottky barrier of 0.35 eV. Furthermore, our results demonstrate that the electric fields and vertical strains can be effectively used to tune both the contact types and the Schottky barrier height of Graphene/WSeTe heterostructure from the p-type Schottky contact to n-type one or to p-type Ohmic contact. Our results could provide a significant guidance for understanding the physical properties of the Graphene/WSeTe heterostructure towards nanoelectronic and optoelectronic devices.

Janus PtSSe and graphene heterostructure with tunable Schottky barrier

Janus transition metal dichalcogenides with a built-in structural cross-plane asymmetry have recently emerged as a new class of two-dimensional materials with a large cross-plane dipole. By using the density functional theory calculation, we report the formation of different Schottky barriers for Janus PtSSe and graphene based van der Waals heterostructures, where the Schottky barrier height (SBH) and type of contact can be controlled by adjusting the interlayer distance, by applying an external electric field, and by having multiple layers of Janus PtSSe. It is found that the effects of tuning are more prominent for SPtSe/graphene as compared to SePtS/graphene. Besides, a transition from n-type Schottky contact to p-type Schottky contact and to Ohmic contact is also observed in the SPtSe/Gr heterostructure for different SPtSe stackings from 1 layer, to 2- and 3-layers, respectively. Our findings indicate that the SPtSe/graphene heterostructure is a suitable candidate for applications that require a tunable SBH.

High-Performance Schottky-Barrier Field-Effect Transistors Based on Monolayer SiC Contacting Different Metals

Schottky-barrier field-effect transistors (SBFETs) based on monolayer SiC contacting four metals (Ag, Au, Al, and Pd) have been proposed using density functional theory and ab initio simulations. The n-type Schottky contacts could be formed between monolayer SiC and Ag, Au electrodes with electron Schottky barrier heights (SBHs) of 0.7 and 1.1 eV, respectively, whereas the p-type Schottky contacts were formed between monolayer SiC and Al, Pd electrodes with hole SBHs of 1.0 and 0.1 eV, respectively. When the gate length was equal to 5.1 nm, SiC-SBFETs with four metals could all overcome the short-channel effect due to the wide bandgap of SiC. In addition, the SiC-SBFET with Pd electrode provided the best performance and could satisfy the performance requirement of high-performance transistor with gate length of 5.1 nm outlined by the International Technology Roadmap for Semiconductors (ITRS). Our study gives an insight into the monolayer SiC–metal interfaces and, thus could be developed into a viable 5-nm “More than Moore” device in the future.

Strain tunable Schottky barriers and tunneling characteristics of borophene/MX2 van der Waals heterostructures

Based on first-principle calculations, we report the strain induced changes in electronic properties and their influence on current-voltage ( I − V ) characteristics of the borophene (β 12 )/MX 2 (M = Mo, W and X = S, Se) vdW heterostructures. The results reveal that the intrinsic electronic nature of borophene and MX 2 is retained because of weak van der Waals interactions. However, p-type Schottky contacts are formed at the interface of the heterostructures. Application of the in-plane tensile and compression strains is effective in tuning the Schottky contacts and controlling the SBHs. Also, at the vertical pressure values of 5.46 and 5.25 GPa for β 12 /MoS 2 and β 12 /WS 2 respectively, Schottky contact changes from p-type to n-type. The I − V characteristics exhibit an ohmic behavior at low bias ± 0.1 V and noticeable NDR on changing positive (negative) biases. Such strain tunable Schottky barriers may be influential in β 12 /MX 2 based high-performance nano- and optoelectronic devices.

Tunable Electronic Properties of Graphene/g-AlN Heterostructure: The Effect of Vacancy and Strain Engineering.

The structural and electronic properties of graphene/graphene-like Aluminum Nitrides monolayer (Gr/g-AlN) heterojunction with and without vacancies are systematically investigated by first-principles calculation. The results prove that Gr/g-AlN with nitrogen-vacancy (Gr/g-AlN-VN) is energy favorable with the smallest sublayer distance and binding energy. Gr/g-AlN-VN is nonmagnetic, like that in the pristine Gr/g-AlN structure, but it is different from the situation of g-AlN-VN, where a magnetic moment of 1 μB is observed. The metallic graphene acts as an electron acceptor in the Gr/g-AlN-VN and donor in Gr/g-AlN and Gr/g-AlN-VAl contacts. Schottky barrier height by traditional (hybrid) functional of Gr/g-AlN, Gr/g-AlN-VAl, and Gr/g-AlN-VN are calculated as 2.35 (3.69), 2.77 (3.23), and 1.10 (0.98) eV, respectively, showing that vacancies can effectively modulate the Schottky barrier height. Additionally, the biaxial strain engineering is conducted to modulate the heterojunction contact properties. The pristine Gr/g-AlN, which is a p-type Schottky contact under strain-free condition, would transform to an n-type contact when 10% compressive strain is applied. Ohmic contact is formed under a larger tensile strain. Furthermore, 7.5% tensile strain would tune the Gr/g-AlN-VN from n-type to p-type contact. These plentiful tunable natures would provide valuable guidance in fabricating nanoelectronics devices based on Gr/g-AlN heterojunctions.

Dependence of channel thickness on MoTe2 transistor performance with Pt contact on a HfO2 dielectric

We investigated the dependence of MoTe2 thickness on it is electrical properties by fabricating several transistors with channel thickness between ∼6 layers and ∼46 layers. The transistor with ∼10-layer channel has the highest hole current, whereas the electron current shows monotonically increase with channel thickness. The measurements of Ids–Vds and temperature dependence show ohmic contact of p-type conduction and Schottky contact of n-type conduction. Thus, the highest hole current is observed in ∼10-layer MoTe2 due to the highest mobility. However, the bandgap of MoTe2 decreases with it is thickness, leading to the reduce of Schottky barrier and the increase of electrons current.

Theoretical Insights into Two-Dimensional IV-V Compounds: Photocatalysts for the Overall Water Splitting and Nanoelectronic Applications.

Two-dimensional (2D) materials have attracted enormous attention in many fields because of their appealing performances. In this contribution, we perform first-principles calculations on the photocatalytic properties of IV-V compounds, along with the design of a functional Schottky device based on a graphene/SiAs van der Waals heterostructure (vdWH). Our results indicate that eight IV-V compound materials are all excellent photocatalysts for water-splitting reactions with high efficiency of visible light, with the conduction band minimum (CBM) and valence band maximum (VBM) both involving the corresponding band-gap region. It is examined whether a weak acid environment is beneficial for the hydrogen production process. Monolayer GeAs is characterized by an excellent absorption coefficient of up to 105-2 × 105 cm-1 in the visible region. The other nanostructures also have a considerable optical absorption as high as approximately half of 105 cm-1. These illustrate fascinating application prospectives for IV-V compounds in photocatalysis for water splitting under the irradiation of visible light, predicting tremendous significance in the fields of energy conversion and hydrogen production. The graphene/SiAs vdWH nanocomposite at the equilibrium state is featured for an n-type Schottky contact. External strain and electric-field applications are employed to practically present the transition for interface contact between the n- and p-type Schottky contacts or between the Schottky and ohmic contacts, which suggests appealing applications for the graphene/SiAs vdWH as a competitive candidate for functional Schottky devices and nanoelectronic materials.

Submicron Size Schottky Junctions on As-Grown Monolayer Epitaxial Graphene on Ge(100): A Low-Invasive Scanned-Probe-Based Study.

We report on the investigation of the Schottky barrier (SB) formed at the junction between a metal-free graphene monolayer and Ge semiconductor substratein the as-grown epitaxial graphene/Ge(100) system. In order to preserve the heterojunction properties, we defined submicron size graphene/Ge junctions using the scanning probe microscopy lithography in the local oxidation configuration, a low-invasive processing approach capable of inducing spatially controlled electrical separations among tiny graphene regions. Characteristic junction parameters were estimated from I-V curves obtained using conductive-atomic force microscopy. The current-voltage characteristics showed a p-type Schottky contact behavior, ascribed to the n-type to p-type conversion of the entire Ge substrate due to the formation of a large density of acceptor defects during the graphene growth process. We estimated, for the first time, the energy barrier height in the as-grown graphene/Ge Schottky junction (φB ≈ 0.45 eV) indicating an n-type doping of the graphene layer with a Fermi level ≈ 0.15 eV above the Dirac point. The SB devices showed ideality factor values around 1.5 pointing to the high quality of the heterojunctions.

Graphene/GeTe van der Waals heterostructure: Functional Schottky device with modulated Schottky barriers via external strain and electric field

Vertical heterogeneous combinations of two-dimensional (2D) materials have been evident as an effective strategy to design novel photovoltaic and optoelectronic devices. Herein, we perform the first-principles calculations about electronic and optical properties of graphene/GeTe van der Waals heterostructures (vdWHs), accompanied by the efficient modulations about Schottky barriers via an external strain and electric field. A slightly opened band gap of 2.0 meV is obtained for graphene/GeTe vdWH in the equilibrium configuration, and the Dirac point is well preserved at K point. The built-in electric field caused by the charge transfer is devoted to its visible contribution to the efficient hindrance for photoexcited electron-hole pair recombination, consequently increasing the number of carriers and extending their lifetimes. The graphene/GeTe vdWH possesses enhanced optical absorption in the visible region in contrast to the separate GeTe monolayer, indicating its significant potential applications in optoelectronic devices. Besides, the graphene/GeTe vdWH at the equilibrium state exhibits an n-type Schottky contact with n-type Schottky barrier height (SBH) of 0.684 eV. By applying suitable external vertical strains or electric fields, the SBHs can be efficiently tuned, making it of significant possibility to realize the transportations between p-type Schottky contact and n-type Schottky contact, and between Schottky contact and Ohmic contact at the graphene/GeTe interface. These findings together predict the graphene/GeTe vdWH nanocomposite as a competitive candidate in next-generation optoelectronics and Schottky devices.

First-principles study of metal-semiconductor contact between MX2 (M = Nb, Pt; X = S, Se) monolayers

First principles calculations are performed to investigate the structural and electronic properties of MX2 (M = Nb, Pt; X = S, Se) monolayers and their van der Waals (vdW) heterostructures. The dynamical stability of monolayers and vdW heterostructures is confirmed by binding energy and phonon spectra. An indirect band gap nature is found for PtS2 and PtSe2 monolayers while NbS2, NbSe2 and all vdW heterostructures are metals. The intrinsic electronic properties of both NbX2 and PtX2 are well preserved due to weak vdW contact. It is demonstrated that a p-type Schottky contact with a small barrier height is formed at NbX2-PtX2 interface. The zero tunnel barrier and higher potential drop across the interface in these contacts imply large transfer of charge carriers across the interface, making them potential candidates in nanoelectronic device applications.

Schottky barrier modulation of a GaTe/graphene heterostructure by interlayer distance and perpendicular electric field

Two-dimensional materials have recently been the focus of extensive research. Graphene-based vertical van der Waals heterostructures are expected to design and fabricate novel electronic and optoelectronic devices. Monolayer gallium telluride is a graphene-like nanosheet synthesized in experiment. Here, the electronic properties of GaTe/graphene heterostructures are investigated under the interlayer coupling and the applied perpendicular electric field. The results show that the electronic properties of GaTe and graphene are preserved, and the energy bandgap of graphene is opened to 13.5 meV in the GaTe/graphene heterostructure. It is found that the n-type Schottky contact is formed in the GaTe/graphene heterostructure, which can be tuned by the interlayer coupling, and the applied electric field. Moreover, a transformation from n-type to p-type Schottky contact is observed when the interlayer distance is smaller than 3.15 Å or the applied electric field is larger than 0.05 V Å−1. These properties are fundamental to the design of new Schottky nanodevices based on the GaTe/graphene heterostructure.

Tri-layered van der Waals heterostructures based on graphene, gallium selenide and molybdenum selenide

In this work, we propose ultrathin trilayered heterostructures (TL-HTSs) of graphene (G), gallium selenide (GaSe), and molybdenum selenide (MoSe2) monolayers and investigate their structural and electronic properties in the framework of first-principles calculations. By calculating the binding energies and interlayer distances and comparing them with those of the typical vdW HTSs, we find that the systems we consider are energetically stable and are characterized by weak vdW interactions. The formation of G, GaSe, and MoSe2 monolayers to form G/GaSe/MoSe2, GaSe/G/MoSe2, and G/MoSe2/GaSe HTSs leads to the opening of a sizable bandgap in graphene at the Dirac point and shows the p-type Schottky contact. Among these kinds of TL-HTSs, the G/GaSe/MoSe2 has many more advantages than the others due to the lowest binding energy of −29.47meV/Å2, the biggest bandgap opening in G of 84.7 meV, and the smallest Schottky barrier height of 0.63 eV. Furthermore, we find that the p-type Schottky contact of G/GaSe/MoSe2 HTS can be turned into an n-type one or into an Ohmic contact when vertical strain or electric field is applied. These results show a potential candidate of the combined HTSs of G, GaSe, and MoSe2 monolayers for developing high speed nanoelectronic and optoelectronic devices.

Bilayer tellurene–metal interfaces

Tellurene, an emerging two-dimensional chain-like semiconductor, stands out for its high switch ratio, carrier mobility and excellent stability in air. Directly contacting the 2D semiconductor materials with metal electrodes is a feasible doping means to inject carriers. However, Schottky barrier often arises at the metal–semiconductors interface, impeding the transport of carriers. Herein, we investigate the interfacial properties of BL tellurene by contacting with various metals including graphene by using ab initio calculations and quantum transport simulations. Vertical Schottky barriers take place in Ag, Al, Au and Cu electrodes according to the maintenance of the noncontact tellurene layer band structure. Besides, a p-type vertical Schottky contact is formed due to the van der Waals interaction for graphene electrode. As for the lateral direction, p-type Schottky contacts take shape for bulk metal electrodes (hole Schottky barrier heights (SBHs) ranging from 0.19 to 0.35 eV). Strong Fermi level pinning takes place with a pinning factor of 0.02. Notably, a desirable p-type quasi-Ohmic contact is developed for graphene electrode with a hole SBH of 0.08 eV. Our work sheds light on the interfacial properties of BL tellurene based transistors and could guide the experimental selections on electrodes.

Tunable Schottky barrier in van der Waals heterostructures of graphene and hydrogenated phosphorus carbide monolayer: first-principles calculations

Atomically thin phosphorus carbide (PC) layers with intriguing electronic and optical properties are promising two-dimensional (2D) materials for electronic and optoelectronic applications. Herein, we first explore the performance of 2D hydrogenated PC monolayers as a channel material contacting with graphene (G) to form van der Waals heterostructures using first-principles calculations. Two PCH (hydrogenation to C)/G and HPC (hydrogenation to P)/G heterostructures are investigated. Results reveal that the electronic properties of constituent layers are well preserved in heterostructures, and a p-type Schottky contact with small Schottky barrier height (SBH) are formed at their interfaces. Interestingly, the Schottky type (n-type and p-type), SBH, and contact types (Schottky contact and Ohmic contact) at the interface can be tuned by external electric field. This work would open a new avenue for applications of 2D PC-based heterostructure devices in future nanoelectronics and optoelectronics.

Tunable electronic properties of van der Waals heterostructures composed of stanene adsorbed on two-dimensional, graphene-like nitrides

We investigated the structural stability and electronic properties of stanene/graphene-like nitride (stanene/XN, X=Al, B, and Ga) heterostructures using first-principles calculations. The results reveal that stanene interacts with BN (GaN) via van der Waals interactions with a binding energy of 93 meV (171 meV) per Sn atom. In contrast, the stanene/AlN heterostructure shows a strong interlayer coupling, with a binding energy of 315 meV per Sn atom. The electronic structure of stanene/GaN shows a direct bandgap of 213 meV at the Dirac point. The stanene/AlN and stanene/GaN heterostructures have Schottky barriers of 1.383 and 1.243 eV, respectively, with p-type Schottky contacts. In addition, an n-type Schottky contact is formed in the stanene/BN heterostructure with a Schottky barrier of 2.812 eV. The results suggest that the studied heterostructures are potential candidates for stanene-based nanoelectronic applications.

Tunable Schottky barrier in graphene/graphene-like germanium carbide van der Waals heterostructure

The structural and electronic properties of van der Waals (vdW) heterostructrue constructed by graphene and graphene-like germanium carbide were investigated by computations based on density functional theory with vdW correction. The results showed that the Dirac cone in graphene can be quite well-preserved in the vdW heterostructure. The graphene/graphene-like germanium carbide interface forms a p-type Schottky contact. The p-type Schottky barrier height decreases as the interlayer distance decreases and finally the contact transforms into a p-type Ohmic contact, suggesting that the Schottky barrier can be effectively tuned by changing the interlayer distance in the vdW heterostructure. In addition, it is also possible to modulate the Schottky barrier in the graphene/graphene-like germanium carbide vdW heterostructure by applying a perpendicular electric field. In particular, the positive electric field induces a p-type Ohmic contact, while the negative electric field results in the transition from a p-type to an n-type Schottky contact. Our results demonstrate that controlling the interlayer distance and applying a perpendicular electric field are two promising methods for tuning the electronic properties of the graphene/graphene-like germanium carbide vdW heterostructure, and they can yield dynamic switching among p-type Ohmic contact, p-type Schottky contact, and n-type Schottky contact in a single graphene-based nanoelectronics device.

Tailoring electronic properties and Schottky barrier in sandwich heterostructure based on graphene and tungsten diselenide

Graphene based two-dimensional layered materials are attracting wide attention both experimentally and theoretically and show many superior properties that individual layers may not hold. In this work, we study theoretically the electronic properties of the graphene/WSe2 van der Waals heterobilayer using the first-principle calculations. Our results demonstrate that the intrinsic electronic properties of graphene and WSe2 monolayer are quite well preserved due to the weak van der Waals interactions. We find that the graphene/WSe2 heterobilayer forms a p-type Schottky contact with the Schottky barrier height of 0.60 eV and shows a good thermoelectric material with high Seebeck coefficient at room temperature. Moreover, the p-type Schottky contact of the graphene/WSe2 heterobilayer can be tailored by inserting WSe2 monolayers to form graphene/WSe2/WSe2 and WSe2/graphene/WSe2 heterotrilayers or by applying electric field perpendicular to the heterobilayer. The p-type Schottky barrier decreases with the insertion of the WSe2 layers, whereas it can be transformed to the n-type one when the negative electric field of −1.5 V/nm is applied. The results reveal the physical nature of the van der Waals heterostructures based on graphene and other two-dimensional transition metal dichalcogenides, which are helpful in providing a route to design graphene-based high-performance optoelectronic nanodevices, such as Schottky diodes and interlayer tunneling field-effect transistors.

Graphene/g-GeC bilayer heterostructure: Modulated electronic properties and interface contact via external vertical strains and electric fileds

Using DFT calculations, we perform the modulated electronic properties and interface contact in the graphene/GeC heterostructure by tuning the interlayer spacing, along with the application of an external electric field. The graphene/GeC interface is examined to be dominated by the van der Waals (vdW) force with equilibrium interlayer spacing of 3.413 Å and binding energy per C atom of approximately −50 meV. This indicates graphene/GeC nanostructure a type of vdW heterostructure (vdWH). A direct band gap up to 6 meV is opened at the Dirac point, with the Dirac point well preserved, suggesting its significant application as a suitable candidate in nano-electronic and optoelectronic devices. Moreover, the graphene/GeC vdWH forms a p-type Schottky contact at the equilibrium state with a Schottky barrier height (SBH) of 0.14 eV. A transition for the interface contact from Schottky to Ohmic can be achieved by modifying the interlayer spacing smaller than 3.20 Å or applying a positive electric field of 0.1–0.7 V Å−1. Interestingly, the p-type SBH (1.00 eV) can be tailored extensively approaching to the n-type SBH (1.09 eV) when negative electric field strengthened to 0.63 V Å−1, demonstrating it substantial potential for the transition of Schottky contact from p-type to n-type. The findings are crucial for designing new nano-electronic devices comprising graphene-based vdWHs, which ascribes to the feasibility for application of tunable vertical strain and electric field in industrial applications.

Dipole controlled Schottky barrier in the blue-phosphorene-phase of GeSe based van der Waals heterostructures.

Controlling the interface structure is of utmost importance to regulating the nanoscale Schottky barrier height (SBH). Herein, by using first-principles calculations, the electronic properties of the graphene (G) based blue-phosphorene-phase of GeSe van der Waals (vdW) heterostructures, including M/G and X/G interfaces (M = Ge; X = Se), are systematically investigated. When the layer spacing exceeds the vdW gap, n-type Schottky contacts are formed for both MX/G and XM/G heterojunctions. With the layer spacing decreasing to equilibrium distances, due to different charge transfer across the interface, MX/G and XM/G heterojunctions display n- and p-type Schottky contacts, respectively. Further decreasing the layer distance makes both heterojunctions transit into p-type ones. The layer-spacing-dependent SBHs can be rationalized by the increased charge transfer across the interface and the resulting interfacial dipole enhancement. Enlightened by the finding of dipole-controlled SBHs, using MX as building blocks, two different stacking patterns, i.e., nMX-MX-G and nXM-XM-G (n = 1 and 2), are designed to further modulate the SBH. Interestingly, due to the presence of the intrinsic dipole of MX, it is found that the magnitude and orientation of the interfacial dipole can be artificially engineered. With n increasing from 0 to 2, nMX-MX-G with an X/G interface changes from the n-type Schottky contact to Ohmic contact. The Fermi level meets the conduction band and G shows a p-type doping feature finally. Likewise, transition from p-type Schottky contact to Ohmic contact is observed for the nXM-XM-G with M/G interface, accompanied by the Fermi level touching the valence band and the feature of n-type doping for G. The role of nMX stacking seems like the role of applying an external electric field (E-field): applying positive E-field is equivalent to the increase of dipole moment while negative E-field corresponds to the offset of dipole moment. In brief, the SBHs of GeSe/G contact are found to be tunable which originates from the intrinsic dipole of MX. The predictable SBHs for these kinds of charming built-in dipole systems are expected to be highly desirable in electronic devices.

Interfacial interaction and Schottky contact of two-dimensional WS<sub>2</sub>/graphene heterostructure

Two-dimensional (2D) materials exhibit massive potential in research and development in the scientific world due to their unique electrical, optical, thermal and mechanical properties. Graphene is an earliest found two-dimensional material, which has many excellent properties, such as high carrier mobility and large surface area. However, single layer graphene has a zero band gap, which limits its response in electronic devices. Unlike graphene, the transition metal sulfides (TMDs) have various band structures and chemical compositions, which greatly compensate for the defect of zero gap in graphene. The WS<sub>2</sub> is one of the 2D TMDs exhibiting a series of unique properties, such as strong spin-orbit coupling, band splitting and high nonlinear susceptibility, which make it possess many applications in semiconducting optoelectronics and micro/nano-electronics. The 2D semiconductors along with semimetallic graphene are seen as basic building blocks for a new generation of nanoelectronic devices. In this way, the artificially designed TMD heterostructure is a promising option for ultrathin photodetectors. There are few reports on the physical mechanism of carrier mobility and charge distribution at the interface of WS<sub>2</sub>/graphene heterostructure, by varying the interfacial distance of WS<sub>2</sub>/graphene heterostructure to investigate the effect on the electronic properties. Here in this work, the corresponding effects of interface cohesive interaction and electronic properties of WS<sub>2</sub>/graphene heterostructure are studied by first-principles method. The calculation results indicate that the lattice mismatch between monolayer WS<sub>2</sub> and graphene is low, the equilibrium layer distance <i>d</i> of about 3.42 Å for the WS<sub>2</sub>/graphene heterostructure and a weak van der Waals interaction forms in interface. Further, by analyzing the energy band structures and the three-dimensional charge density difference of WS<sub>2</sub>/graphene, we can identify that at the interface of the WS<sub>2</sub> layer there appears an obvious electron accumulation: positive charges are accumulated near to the graphene layer, showing that WS<sub>2</sub> is an n-type semiconductor due to the combination with graphene. Furthermore, the total density of states and corresponding partial density of states of WS<sub>2</sub>/graphene heterostructure are investigated, and the results show that the valence band is composed of hybrid orbitals of W 5d and C 2p, whereas the conduction band is comprised of W 5d and S 3p orbitals, the orbital hybridization between W 5d and S 3p will cause photogenerated electrons to transfer easily from the internal W atoms to the external S atoms, thereby forming a build-in internal electric field from graphene to WS<sub>2</sub>. Finally, by varying the interfacial distance for analyzing the Schottky barrier transition, as the interfacial distance is changed greatly from 2.4 Å to 4.2 Å, the shape of the band changes slightly, however, the Fermi level descends relatively gradually, which can achieve the transition from a p-type Schottky contact to an n-type Schottky contact in the WS<sub>2</sub>/graphene. The plane-averaged charge density difference proves that the interfacial charge transfer and the Fermi level shift are the reasons for determining the Schottky barrier transition in the WS<sub>2</sub>/graphene heterostructure. Our studies may prove to be instrumental in the future design and fabrication of van der Waals based field effect transistors.