Projected Band Structure Research Articles

Vertical strain-induced modification of the electrical and spin properties of monolayer MoSi2 X 4 (X = N, P, As and Sb)

In this work, the electrical and spin properties of monolayer MoSi2 X 4 (X = N, P, As, and Sb) under vertical strain are investigated. The band structures show that MoSi2N4 is an indirect semiconductor, whereas other compounds are direct semiconductors. The vertical strain has been selected to modify the electrical properties. The bandgap shows a maximum and decreases for both tensile and compressive strains. The valence band at K-point displays a large spin-splitting, whereas the conduction band has a negligible splitting. On the other hand, the second conduction band has a large spin-splitting and moves down under vertical strain which leads to a large spin-splitting in both conduction and valence bands edges. The projected density of states along with the projected band structure clarifies the origin of these large spin-splittings. These three spin-splittings can be controlled by vertical strain.

Valley Polarization in Monolayer Ferromagnetic FeCl: A First‐Principles Study

Phys. Status Solidi RRL 2020, 14, 2000206 DOI: 10.1002/pssr.202000206 In the published article, it was reported that 2D FeCl can realize the valley Hall effect, and that the valley polarization comes from the opposite signs of the Berry curvatures around the two valleys (B and B′) on the high-symmetry lines Γ–X and Γ–X′. However, it is now realized that the distribution of the Berry curvatures of FeCl should match with its crystal symmetry. The distribution of the Berry curvatures reported violates this rule because FeCl has C4 symmetry, which requires the same signs for the Berry curvatures around the valleys B and B′. After analyzing all calculation processes in detail, an error is found in the step of calculating the maximal localized Wannier functions (MLWFs). Although the energy bands from the MLWFs match with the results of first-principles calculations, the C4 symmetry is broken for low-energy electronic states and the Berry curvatures. After analyzing the influence of C4 rotation symmetry to the distributions of the Berry curvatures, it is found that the Chern number must be 2 or −2 for FeCl. To obtain the correct results of the Berry curvatures, a tight-binding model is built with the basis of the five d orbitals of the Fe atom, and this model matches with the crystal symmetry of FeCl. According to the orbital projected band structures without spin–orbit coupling (SOC) in the published article, the main contribution to the spin-polarized bands around the Fermi level is from the five d orbitals of the Fe atoms. Thus, we constructed a five-band tight-binding Hamiltonian with the basis set of the five spin-down d orbitals. Figure 1a herein shows the band structure from the tight-binding model and first-principles calculation, and they match with each other. To consider the effect of SOC, we add an intrinsic SOC term into this Hamiltonian. The hopping strength of SOC is set to 0.05 eV to match the bandgap (20 meV) of the first-principles result (see Figure 1b). The broken time-reversal symmetry generally results in the nonvanishing Berry curvatures for the electronic states below the Fermi level. With the help of the above tight-binding model, we calculated the Berry curvatures in the first Brillouin zone (see Figure 1c) and the anomalous Hall conductivity (see Figure 1d). It is shown that the Berry curvatures have the same signs around B and B′. By integrating the Berry curvatures near the valleys B and B′, we obtain Chern numbers of CB and CB′, and they are approximately equal to −1/2, which indicates VHE cannot happen if only a proper electronic field is applied.[1] To induce valley polarization from FeCl, we apply uniaxial strain to break the energy degeneracy of the valleys B and B’. The energy splittings of the different valleys are very important for the applications of FeCl in valleytronics. For 2D FeCl (see Figure 2c herein), the bands of the different valleys (B and B′) have the same energies for unstrained FeCl and the energy degeneracy is protected by the C4 rotation symmetry and Mx(y) mirror symmetries of the point group D4h.[2, 3] Valleys B and B′ are related by C4 symmetry, which leads to similar Berry curvature distributions around B and B′. Meanwhile, due to the existence of C 4 2 or Mx(y), the Berry curvatures of the four valleys have same signs in the first Brillouin zone, as shown in Figure 1c. If symmetries are broken by uniaxial strains, the point group becomes D2h, which only has C2 symmetry and Mx(y) mirror symmetry. Therefore, the Berry curvatures around valleys B and B′ can be different. It is worth mentioning that the Berry curvature distribution of the two valleys in kx = 0 or ky = 0 should remain the same and it is protected by C2 and Mx(y). We find the size of movement for the energies of valley B and B′ almost linearly dependent on the strain. When −5% strain is applied (see Figure 2b), the energy of valley B′ moves to above the Fermi level (+0.04 eV); at the same time, the energy of B moves to −0.11 eV. If the Fermi level is tuned to these two energies, a valley polarized current would be produced. Moreover, as shown in Figure 2d, the tensile strain can induce the opposite movement on the energies of B and B′. Our results revealed that uniaxial strain can effectively adjust the energies of different valleys and induce valley polarization in 2D FeCl.

Lattice and electronic structures of BAlN in the deep ultraviolet spectral region

BAlN exhibit intriguing properties for both fundamental research and potential application in optoelectronic devices operating in the deep ultraviolet spectral ranges. For BxAl1-xN, the crystal lattice constant derived for the whole range of the alloy composition closely follows Vegard's law. The mechanical stability is represented by elastic constants. The fundamental bandgap is converted from direct in AlN to indirect in BN. The orbital projected band structure of BAlN is obtained to gain insight into the electronic structure and the optical anisotropy with favorable light polarization is understood in terms of the crystal field split-off energy. The band structure parameters including the band gap, the effective masses of electrons and holes are presented and the corresponding electron mobility of BAlN with the direct band gap are predicted to be larger than that of AlN. It is worth noting that BAlN with the direct band gap are quite promising for application in electronic and optoelectronic devices operating in the UVC range.

Anisotropic strain effect on structural and electronic properties in WSe2/ZnO mixed-dimensional heterostructure

Mixed-heterostructures have received much attention due to their broader application in functional devices. Here, we investigate the strain effect on structural and electronic properties of 2D WSe2/1D ZnO nanoribbon (WSe2/ZnO-NR) mixed-dimensional heterostructure including the armchair ZnO nanoribbon (a-ZnO-NR) and zigzag ZnO nanoribbon (z-ZnO-NR) on WSe2 layer by using the first principles calculation. The results show that the binding strength of WSe2/ZnO-NR is enhanced. Remarkably, the WSe2/ZnO-NR presents anisotropic electronic properties under strain effect. Firstly, whether the WSe2/a-ZnO-NR is passivated by hydrogens or not, they always show type-I direct band gap alignment. After the strain applied, the band structures are transformed into type-II band alignment, promoting the separation of photogenerated electron-hole pairs. For WSe2/z-ZnO-NR, it exhibits type-II band alignment. The strain engineering can effectively modulate the band gap of WSe2/z-ZnO-NR. When the edge of z-ZnO-NR is not passivatied, the WSe2/z-ZnO-NR shows spin polarized band structure with a narrow gap. The band gap and spin polarization can be tuned by strain. The projected band structures reveal that the WSe2/z-ZnO-NR not only forms type-II band alignment, but also realizes the separation of different spin states. This work provides useful guide for designing photoelectronic devices experimentally.

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Type-II Dirac points and edge transports in phononic crystal plates

The accidentally degenerate type-II Dirac points in sonic crystal has been realized recently. However, elastic phononic crystals with type-II Dirac points have not yet been explored. In this work, we design a two-dimensional phononic crystal plate in square lattice with type-II Dirac points for elastic waves. The type-II Dirac points, different from the type-I counterparts, have the tiled dispersions and thus the iso-frequency contours become crossed lines. By tuning structures to break the mirror symmetry, the degeneracies of the type-II Dirac points are lifted, leading to a band inversion. In order to have a further explanation, we also calculate the Berry curvatures of phononic crystals with opposite structure parameters, and it turns out that these two crystals hold opposite signs around the valley. The phononic crystal plates before and after the band inversion belong to different topological valley phases, whose direct consequence is that the topologically protected gapless interface states exist between two distinct topological phases. Topologically protected interface states are found by calculating the projected band structures of a supercell that contains two kinds of interfaces between two topological phases. Robustness of the interface transport is verified by comparing the transmission rate for perfect interface with that for defective interface. Moreover, owing to the special stress field distributions of the elastic plate waves, the boundaries of a single phononic crystal phase can similarly host the gapless boundary states, which is found by calculating the projected band structures of a supercell with a single phase, thus having two free boundaries on the edges. This paper extends the two-dimensional Dirac points and valley states in graphene-like systems to the type-II cases, and obtains in the same structure the gapless interface and boundary propagations. Owing to the simple design scheme of the structure, the phononic crystal plates can be fabricated and scaled to a small size. Our system provides a feasible way of constructing high-frequency elastic wave devices.

Theoretical investigation on stability and electronic properties of Janus MoSSe nanotubes for optoelectronic applications

The Janus MoSSe has attracted much attention since its successful synthetization in experiment. Due to the inversion symmetry breaking in vertical direction, it has an inner-built electric field and has potential applications in many fields such as optoelectronic devices and photocatalysis. Although its two-dimensional form has been widely investigated, the properties of Janus MoSSe nanotube has not been systematically investigated. In this work, we calculated the formation energy and projected band structure of Janus MoSSe nanotube with first principle calculation. Different morphologies such as singe wall nanotube and double wall nanotube are considered. Other factors such as the position of S atom and Se atom and the radius of nanotube are also considered. As last, we proved that the band structure is robust under rotation operation and translation operation. This work will shed some lights on the application of Janus MoSSe nanotube in optoelectronic field.

Electronic properties of Bi2Se3 dopped by 3d transition metal (Mn, Fe, Co, or Ni) ions

Topological insulators are characterized by the existence of band inversion and the possibility of the realization of surface states. Doping with a magnetic atom, which is a source of the time-reversal symmetry breaking, can lead to realization of novel magneto-electronic properties of the system. In this paper, we study effects of substitution by the transition metal ions (Mn, Fe, Co and Ni) into Bi2Se3 on its electric properties. Using the ab inito supercell technique, we investigate the density of states and the projected band structure. Under such substitution the shift of the Fermi level is observed. We find the existence of nearly dispersionless bands around the Fermi level associated with substituted atoms, especially, in the case of the Co and Ni. Additionally, we discuss the modification of the electron localization function as well as charge and spin redistribution in the system. Our study shows a strong influence of the transition metal-Se bond on local modifications of the physical properties. The results are also discussed in the context of the interplay between energy levels of the magnetic impurities and topological surface states.

CuTe chains on Cu(111) by deposition of one-third of a monolayer of Te: Atomic and electronic structure

The surface atomic and electronic structure after deposition of 1/3 monolayer (ML) Te on Cu(111) was determined using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy and spectroscopy (STM/STS), angle-resolved single and two-photon photoelectron spectroscopy (ARPES /AR-2PPE) and density functional theory (DFT) calculations. Contrary to the current state in literature Te does not create a two-dimensional surface alloy but forms Cu$_2$Te$_2$ adsorbate chains in a $\left(2\sqrt{3} \times \sqrt{3}\right)\textrm{R30}^\circ$ superstructure. We establish this by a high-precision LEED-IV structural analysis with Pendry $R$ factor of $R = 0.099$ and corroborating DFT and STM results. The electronic structure of the surface phase is dominated by an anisotropic downward dispersing state at the Fermi energy $E_F$ and a more isotropic upward dispersing unoccupied state at $E-E_F = + 1.43\,\textrm{eV}$. Both states coexist with bulk states of the projected band structure and are therefore surface resonances.

Electron correlation induced orbital selective Lifshitz transition in new hybrid 12442 iron based superconductors

A systematic detailed electronic structure study of the newly discovered ACa2Fe4As4F2i.e., 12442 iron based compounds (where A = K, Rb, Cs) within density functional theory (DFT) based first principles calculations is presented. The orbital projected band structures reveal mixed multi-orbital multi-band nature of the 12442 compounds having contributions mostly from Fe-3d orbitals. Unlike other hybrid iron based superconductors, contribution of As-4pz orbital is negligible in these compounds. Substitution of alkali atoms of gradually higher atomic radius exert chemical pressure inside the compound and induce orbital selective evolution of band structure as well as density of states. Orbital projected Fermi surfaces divulge orbital selective modification in intra orbital, inter-band nesting condition of the dx2-y2/z2 and dxz/yz orbital derived FSs. Correlation induced orbital selective Lifshitz transition is revealed through GGA+U calculations. The tight binding band structure fitted with low energy DFT bands using maximally localized Wannier functions divulge a unique feature of the nearest neighbor hopping parameter. In contrast to many iron based compounds, intra-orbital hopping in dz2 is larger than intra-orbital hopping in dx2-y2. Orbital selective decrease in intra-orbital hopping of dxy and dyz due to change in chemical pressure induced by substitution of alkali atoms Rb or Cs is revealed in these compounds.

Conical dispersions induced interface states in two-dimensional photonic crystals

It is known that interface states are not guaranteed at the interface between two two-dimensional photonic crystals. To create an interface state, it is usual to decorate the structure near the interface. In this work, we construct a photonic crystal in an oblique lattice through tilting from a square lattice. Conical dispersion, existing in the oblique lattice, induces band inversion and results in two band gaps, separated by the projected band structure of it, possessing opposite signs of surface impedance. Therefore, interface states are guaranteed to exist at the interface between the square lattice and its “tilted” partner.

A promising blue phosphorene/C2N van der Waals type-II heterojunction as a solar photocatalyst: a first-principles study.

An appropriate band structure and effective carrier separation are very important for the performance of a solar photocatalyst. In this paper, based on first-principles calculations, it was predicted that blue phosphorene (BlueP) and a C2N monolayer can form a promising metal-free type-II heterojunction. The electronic structure of the BlueP/C2N heterojunction facilitated the overall water splitting reactions well. The projected band structure showed that the conduction band edge was contributed by C2N and the valence band edge was dominated by BlueP. Under the combination of the driving force of the band offset and the built-in electric field between the two layers, the photo-generated electrons and holes were transferred spontaneously to the conduction band of C2N and the valence band of BlueP, respectively. An effective carrier separation in the heterostructure was thus achieved. More notably, the obtained light absorption of the BlueP/C2N junction showed an obvious red-shift, which greatly extended the area of light adsorption to the visible light region. We further proposed that strain could also be used to modulate the band gap and the band edge positions of the heterojunction. Our results not only provide a theoretical design, but also reveal the fundamental separation mechanism of the photo-generated carriers in the BlueP/C2N heterojunction.

Topologically protected edge states of elastic waves in phononic crystal plates

<sec> The topologically protected edge states of elastic waves in phononic crystal plates have the outstanding characteristics in wave manipulation such as the strong suppression of back-scattering and defect immunity, which can be used for controlling vibration and noise, detecting the structural damage, conducting the material nondestructive test and other engineering practices, and therefore have received much attention. But for plate structures, the propagation of elastic waves is complicated due to the coexistence and coupling of different types of wave modes, resulting in a challenge in designing topologically protected states. </sec><sec>In this paper, a simple phononic crystal plate with triangular holes is designed for elastic wave manipulation based on topologically protected edge states. The band structure characteristics of the unit cell are studied by varying the rotation angle <i>θ</i> of the triangular holes around their geometric centers from the initial positions. It is found that the band structure of the initial unit cell with rotation angle <i>θ</i> = 0° has two pairs of degenerate modes. At <inline-formula><tex-math id="M6">\begin{document}$ \theta = \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.png"/></alternatives></inline-formula>, a double Dirac cone appears at the center <i>Γ</i> point of the Brillouin zone without requiring the lattices to fold, and a band inversion occurs on both sides of <inline-formula><tex-math id="M7">\begin{document}$ \pm 33^\circ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.png"/></alternatives></inline-formula> which can be characterized as a topological phase transition. </sec><sec>The elastic band gap and two kinds of pseudospin states with clockwise or counterclockwise circulating mechanical energy flux patterns in the band structure are found by calculating the projected band structures of a supercell which is composed of phononic crystals with different topological phases. Based on this finding, different constructions of phononic waveguide are used for implementing the numerical analysis to demonstrate the back-scattering immunity of the edge states when disorder, tortuosity and cavity are introduced into the waveguide. Unidirectional robust propagation and multichannel waveguide switch due to the pseudospin-dependent one-way edge modes are also validated with numerical models. The phononic crystal plate presented in this paper provides a simple realizable method of designing the topologically protected elastic edge states. </sec>

Underwater acoustic metamaterial based on double Dirac cone characteristics in rectangular phononic crystals**Project supported by the National Natural Science Foundation of China (Grant Nos. 11602269, 11972034, and 11802213), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB22040301), and the Research Program of Beijing, China (Grant Nos. Z161100002616034 and Z171100000817010).

We theoretically construct a rectangular phononic crystal (PC) structure surrounded by water with C2v symmetry, and then place a steel rectangular scatterer at each quarter position inside each cell. The final complex crystal has two forms: the vertical type, in which the distance s between the center of the scatterer and its right-angle point is greater than 0.5a, and the transverse type, in which s is smaller than 0.5a (where a is the crystal constant in the x direction). Each rectangular scatterer has three variables: length L, width D, and rotation angle θ around its centroid. We find that, when L and D change and θ is kept at zero, there is always a linear quadruply degenerate state at the corner of the irreducible Brillouin zone. Then, we vary θ and find that the quadruply degenerate point splits into two doubly-degenerate states with odd and even parities. At the same time, the band structure reverses and undergoes a phase change from topologically non-trivial to topologically trivial. Then we construct an acoustic system consisting of a trivial and a non-trivial PC with equal numbers of layers, and calculate the projected band structure. A helical one-way transmission edge state is found in the frequency range of the body band gap. Then, we use the finite-element software Comsol to simulate the unidirectional transmission of this edge state and the backscattering suppression of right-angle, disorder, and cavity defects. This acoustic wave system with rectangular phononic crystal form broadens the scope of acoustic wave topology and provides a platform for easy acoustic operation.

A 2D ZnSe/BiOX vertical heterostructure as a promising photocatalyst for water splitting: a first-principles study

A vertical heterostructure is an effective method for regulating the properties of 2D materials that are superior to their individual components due to the interfacial interaction. Here, 2D ZnSe/BiOX (X = Cl, Br, I) vertical heterostructures as potential photocatalysts for water splitting are systematically investigated using first-principles calculations. The results indicate that the binding strength of the heterostructure is larger than −17.6 meV Å−2, favoring its experimental realization. Furthermore, the phonon dispersion and ab initio molecular dynamics (AIMD) analysis also indicate its good dynamical and thermodynamic stability. Remarkably, the ZnSe/BiOX heterostructures form a type-II band alignment with a direct band gap ranging from 1.78 eV to 2.06 eV, which enables the separation of electrons and holes in two different layers upon visible-light irradiation. The ZnSe/BiOX heterostructures also show high electron mobility, leading to fast migration of photogenerated electrons and extension of their lifetimes. The projected band structure, partial density of states, and partial charge densities show that the electrons of the valence band maximum (VBM) and conduction band minimum (CBM) are located at different sides of the ZnSe/BiOX heterostructures. According to the Bader charge analysis and charge density difference, an internal electric field exists across the interface which will effectively promote the separation of the photoinduced electron–hole pairs. The band-edge positions of the ZnSe/BiOX heterostructures have demonstrated that the band levels of the VBM and CBM stride the oxidation and reduction potential for water splitting. In addition, the band gaps and band-edge positions of the ZnSe/BiOX heterostructures can be tuned by the in-layer biaxial strain. Therefore, our results suggest that ZnSe/BiOX heterostructures are a promising potential application for water splitting under visible light as a novel photocatalyst.

Theoretical investigation on electronic and optical properties of the graphene-MoSe2-graphene sandwich heterostructure

We theoretically investigated the structural stability, electronic and optical properties of the sandwich graphene-MoSe2-graphene (G-MoSe2-G) heterostructure via the density functional theory (DFT). The simulation revealed that the relative movement of the layers along the plane can hardly affect the electronic and optical properties, as well as the structural stability. However, both the vertical and biaxial strain applied to the sandwich heterostructure can significantly modify the band structure, which results in the change of electronic and optical properties. We elucidated the mechanism for the band tuning by examining the projected band structure and the charge transfer between graphene and MoSe2 layers. In the meantime, the absorption peak at ∼ 1.3 μm shifted with the increase of the strain. We believe that the sandwich heterostructure can be of great interest for applications as optical modulators, sensors and photodetectors.

Fabrication of chiral channel in three-dimensional photonic crystal using projection microstereolithography

Backscattering-immune propagation is one of the unique characteristics in topological photonic crystals. Such functionality can be realized by constructing a three-dimensional chiral channel in photonic crystals, of which the fabrication process cannot be compatible to complementary metal-oxide-semiconductor lithography. Here, we employed projection microstereolithography to fabricate a three-dimensional chiral channel surrounding in a photonic crystal template with the lattice constant of 462 μm. Both projected band structure and Poynting vector patterns of the three-dimensional chiral channel are numerically calculated. Our work provides a feasible way to fabricate a backscattering-immune waveguide in three-dimensional photonic crystals.

Electronic structure and surface properties ofMgB2(0001) upon oxygen adsorption

We use density-functional theory to investigate the bulk and surface properties of ${\mathrm{MgB}}_{2}$. The unique bonding structure of ${\mathrm{MgB}}_{2}$ is investigated by Bader's atoms-in-molecules, charge density difference, and occupancy projected band structure analyses. Oxygen adsorption on the charge-depleted surfaces of ${\mathrm{MgB}}_{2}$ is studied by a surface potential energy mapping method, reporting a complete map including low-symmetry binding sites. The B-terminated ${\mathrm{MgB}}_{2}$(0001) demonstrates reconstruction of the graphenelike B layer, and the reconstructed geometry exposes a threefold site of the subsurface Mg, making it accessible from the surface. Detailed reconstruction mechanisms are studied by simulated annealing method based on ab initio molecular dynamics and nudged elastic band calculations. The surface clustering of B atoms significantly modifies the B $2p$ states to occupy low energy valence states. The present paper emphasizes that a thorough understanding of the surface phase may explain an apparent inconsistency in the experimental surface characterization of ${\mathrm{MgB}}_{2}$. Furthermore, these results suggest that the surface passivation can be an important technical challenge when it comes to development of a superconducting device using ${\mathrm{MgB}}_{2}$.

Tailoring topological states in silicene using different halogen-passivated Si(111) substrates

We investigate the band structure and topological phases of silicene embedded on halogenated Si(111) surface, by virtue of density functional theory and tight-binding calculations.Our results show that the Dirac character of low energy excitations in silicene is almost preserved in the presence of silicon substrate passivated by various halogens. Nevertheless, the combined effects of charge transfer into the substrate, stretching of bonds between silicon atoms, and symmetry breaking which originates from van der Waals interaction, result in a gap $E_{g1}$ in the spectrum of the embedded silicene. We further take the spin-orbit interaction into account and obtain its strength and the resulting enhancement in the gap $E_{g2}=2\lambda$. Both $E_{g1}$ and $E_{g2}$ which contribute to the total gap, vary significantly when different halogen atoms are used for the passivation of the Si surface and for the case of iodine, they have very large values of $70$ and $23$ meV, respectively. To examine the topological properties, we calculate the projected band structure of silicene from which the tight binding parameters of the low-energy effective Hamiltonian are obtained by fitting. Our results based on Berry curvature and $\mathbb{Z}_2$ invariant reveals that silicene on halogenated Si substrates has a topological insulating state which can survive even at room temperature for the substrate with iodine and bromine at the surface. Similar to the free standing silicene, by applying a perpendicular electric field and at a certain critical value which again depends on the type of halogens, the gap closes and silicene undergoes a transition to a trivial insulating state. As a key finding, we see that the presence of halogenated substrate except for the case of fluorine enhances the robustness of the topological phases against the vertical electric field and most probably other external perturbations.

Interlayer coupling and electric field tunable electronic properties and Schottky barrier in a graphene/bilayer-GaSe van der Waals heterostructure.

In this work, using density functional theory we investigated systematically the electronic properties and Schottky barrier modulation in a multilayer graphene/bilayer-GaSe heterostructure by varying the interlayer spacing and by applying an external electric field. At the equilibrium state, the graphene is bound to bilayer-GaSe by a weak van der Waals interaction with the interlayer distance d of 3.40 Å with the binding energy per carbon atom of -37.71 meV. The projected band structure of the graphene/bilayer-GaSe heterostructure appears as a combination of each band structure of graphene and bilayer-GaSe. Moreover, a tiny band gap of about 10 meV is opened at the Dirac point in the graphene/bilayer-GaSe heterostructure due to the sublattice symmetry breaking. The band gap opening in graphene makes it suitable for potential applications in nanoelectronic and optoelectronic devices. The graphene/bilayer-GaSe heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.72 eV at the equilibrium interlayer spacing. Furthermore, a transformation from the n-type to p-type Schottky contact could be performed by decreasing the interlayer distance or by applying an electric field. This transformation is observed when the interlayer distance is smaller than 3.30 Å, or when the applied positive external electric field is larger than 0.0125 V Å-1. These results are very important for designing new electronic Schottky devices based on graphene and other 2D semiconductors such as a graphene/bilayer-GaSe heterostructure.