Theoretical prediction of electronic properties and contact barriers in a metal/semiconductor NbS2/Janus MoSSe van der Waals heterostructure.

The emergence of van der Waals (vdW) heterostructures, which consist of vertically stacked two-dimensional (2D) materials held together by weak vdW interactions, has introduced an innovative avenue for tailoring nanoelectronic devices. In this study, we have theoretically designed a metal/semiconductor heterostructure composed of NbS2 and Janus MoSSe, and conducted a thorough investigation of its electronic properties and the formation of contact barriers through first-principles calculations. The effects of stacking configurations and the influence of external electric fields in enhancing the tunability of the NbS2/Janus MoSSe heterostructure are also explored. Our findings demonstrate that the NbS2/MoSSe heterostructure is not only structurally and thermally stable but also exfoliable, making it a promising candidate for experimental realization. In its ground state, this heterostructure exhibits p-type Schottky contacts characterized by small Schottky barriers and low tunneling barrier resistance, showing its considerable potential for utilization in electronic devices. Additionally, our findings reveal that the electronic properties, contact barriers and contact types of the NbS2/MoSSe heterostructure can be tuned by applying electric fields. A negative electric field leads to a conversion from a p-type Schottky contact to an n-type Schottky contact, whereas a positive electric field gives rise to a transformation from a Schottky into an ohmic contact. These insights offer valuable theoretical guidance for the practical utilization of the NbS2/MoSSe heterostructure in the development of next-generation electronic and optoelectronic devices.

Tunable Electronic Properties, Carrier Mobility, and Contact Characteristics in Type-II BSe/Sc2CF2 Heterostructures toward Next-Generation Optoelectronic Devices.

Conducting heterostructures have emerged as a promising strategy to enhance physical properties and unlock the potential application of such materials. Herein, we conduct and investigate the electronic and transport properties of the BSe/Sc2CF2 heterostructure using first-principles calculations. The BSe/Sc2CF2 heterostructure is structurally and thermodynamically stable, indicating that it can be feasible for further experiments. The BSe/Sc2CF2 heterostructure exhibits a semiconducting behavior with an indirect band gap and possesses type-II band alignment. This unique alignment promotes efficient charge separation, making it highly promising for device applications, including solar cells and photodetectors. Furthermore, type-II band alignment in the BSe/Sc2CF2 heterostructure leads to a reduced band gap compared to the individual BSe and Sc2CF2 monolayers, leading to enhanced charge carrier mobility and light absorption. Additionally, the generation of the BSe/Sc2CF2 heterostructure enhances the transport properties of the BSe and Sc2CF2 monolayers. The electric fields and strains can modify the electronic properties, thus expanding the potential application possibilities. Both the electric fields and strains can tune the band gap and lead to the type-II to type-I conversion in the BSe/Sc2CF2 heterostructure. These findings shed light on the versatile nature of the BSe/Sc2CF2 heterostructure and its potential for advanced nanoelectronic and optoelectronic devices.

First-principles investigations of metal-semiconductor MoSH@MoS2 van der Waals heterostructures.

Two-dimensional (2D) metal-semiconductor heterostructures play a critical role in the development of modern electronics technology, offering a platform for tailored electronic behavior and enhanced device performance. Herein, we construct a novel 2D metal-semiconductor MoSH@MoS2 heterostructure and investigate its structures, electronic properties and contact characteristics using first-principles investigations. We find that the MoSH@MoS2 heterostructure exhibits a p-type Schottky contact, where the specific Schottky barrier height varies depending on the stacking configurations employed. Furthermore, the MoSH@MoS2 heterostructures possess low tunneling probabilities, indicating a relatively low electron transparency across all the patterns of the MoSH@MoS2 heterostructures. Interestingly, by modulating the electric field, it is possible to modify the Schottky barriers and achieve a transformation from a p-type Schottky contact into an n-type Schottky contact. Our findings pave the way for the development of advanced electronics technology based on metal-semiconductor MoSH@MoS2 heterostructures with enhanced tunability and versatility.

On the impact of adsorbed gas molecules on the anisotropic electro-optical properties of ß12-borophene.

We theoretically study the role of adsorbed gas molecules on the electronic and optical properties of monolayer ß12-borophene with {a,b,c,d,e} atoms in its unit cell. We focus our attention on molecules NH3, NO, NO2, and CO, which provide additional states permitted by the host electrons. Utilizing the six-band tight-binding model based on an inversion symmetry (between {a,e} and {b,d} atoms) and the Kubo formalism, we survey the anisotropic electronic dispersion and the optical multi-interband spectrum produced by molecule-boron coupling. We consider the highest possibilities for the position of molecules on the boron atoms. For molecules on {a,e} atoms, the inherent metallic phase of ß12-borophene becomes electron-doped semiconducting, while for molecules on {b,d} and c atoms, the metallic phase remains unchanged. For molecules on {a,e} and {b,d} atoms, we observe a redshift (blueshift) optical spectrum for longitudinal/transverse (Hall) component, while for molecules on c atoms, we find a redshift (blueshift) optical spectrum for longitudinal (transverse/Hall) component. We expect that this study provides useful information for engineering field-effect transistor-based gas sensors.

Quantum magneto-transport properties of monolayers MoSi2N4, WSi2N4, and MoSi2As4.

We study the transport properties of monolayers MoSi2N4, WSi2N4, and MoSi2As4in a perpendicular magnetic field. The Landau level (LL) band structures including spin and exchange field effects are derived and discussed using a low-energy effective model. We show that the LLs band structures of these materials are similar to those of phosphorene and transition-metal dichalcogenides rather than graphene or silicene. The combination of strong spin-orbit coupling and exchange fields reduces the degradation of the LLs, leading to new plateaus in the Hall conductivity and Hall resistivity and new peaks in the longitudinal conductivity and longitudinal resistivity. The effect of the exchange field, carrier density, and LLs band structure on the conductivities and resistivities have been investigated. At high temperatures, the steps in Hall conductivity and resistivity plateaus disappear and reduce to their corresponding classical forms.

First-principles investigation of a type-II BP/Sc2CF2 van der Waals heterostructure for photovoltaic solar cells.

Constructing heterostructures has proven to be an effective strategy to manipulate the electronic properties and enlarge the application possibilities of two-dimensional (2D) materials. In this work, we perform first-principles calculations to generate the heterostructure between boron phosphide (BP) and Sc2CF2 materials. The electronic characteristics and band alignment of the combined BP/Sc2CF2 heterostructure, as well as the effects of an applied electric field and interlayer coupling, are examined. Our results predict that the BP/Sc2CF2 heterostructure is energetically, thermally and dynamically stable. All considered stacking patterns of the BP/Sc2CF2 heterostructure possess semiconducting behavior. Furthermore, the formation of the BP/Sc2CF2 heterostructure gives rise to the generation of type-II band alignment, which causes photogenerated electrons and holes to move in opposite ways. Therefore, the type-II BP/Sc2CF2 heterostructure could be a promising candidate for photovoltaic solar cells. More interestingly, the electronic properties and band alignment in the BP/Sc2CF2 heterostructure can be tuned by applying an electric field and modifying the interlayer coupling. Applying an electric field not only causes modulation of the band gap, but also leads to the transition from a semiconductor to a gapless semiconductor and from type-II to type-I band alignment of the BP/Sc2CF2 heterostructure. In addition, changing the interlayer coupling gives rise to modulation of the band gap of the BP/Sc2CF2 heterostructure. Our findings suggest that the BP/Sc2CF2 heterostructure is a promising candidate for photovoltaic solar cells.

Understanding Electronic Properties and Tunable Schottky Barriers in a Graphene/Boron Selenide van der Waals Heterostructure.

van der Waals heterostructures provide a powerful platform for engineering the electronic properties and for exploring exotic physical phenomena of two-dimensional materials. Here, we construct a graphene/BSe heterostructure and examine its electronic characteristics and the tunability of contact types under electric fields. Our results reveal that the graphene/BSe heterostructure is energetically, mechanically, and thermodynamically stable at room temperature. It forms a p-type Schottky contact and exhibits a high carrier mobility, making it a promising candidate for future Schottky field-effect transistors. Furthermore, applying an electric field not only reduces contact barriers but also induces a transition from a p-type to an n-type Schottky contact and from a Schottky to an ohmic contact, offering further potential for the control and manipulation of the heterostructure's electronic properties. Our findings offer a rational basis for the design of energy-efficient and tunable heterostructure devices based on the graphene/BSe heterostructure.

Correction: Theoretical prediction of the electronic structure, optical properties and photocatalytic performance of type-I SiS/GeC and type-II SiS/ZnO heterostructures.

[This corrects the article DOI: 10.1039/D3RA01061A.].

Theoretical prediction of the electronic structure, optical properties and photocatalytic performance of type-I SiS/GeC and type-II SiS/ZnO heterostructures.

Nowadays, it would be ideal to develop high-performance photovoltaic devices as well as highly efficient photocatalysts for the production of hydrogen via photocatalytic water splitting, which is a feasible and sustainable energy source for addressing the challenges related to environmental pollution and a shortage of energy. In this work, we employ first-principles calculations to investigate the electronic structure, optical properties and photocatalytic performance of novel SiS/GeC and SiS/ZnO heterostructures. Our results indicate that both the SiS/GeC and SiS/ZnO heterostructures are structurally and thermodynamically stable at room temperature, suggesting that they are promising materials for experimental implementation. The formation of SiS/GeC and SiS/ZnO heterostructures gives rise to reduction of the band gaps as compared to the constituent monolayers, enhancing the optical absorption. Furthermore, the SiS/GeC heterostructure possesses a type-I straddling gap with a direct band gap, while the SiS/ZnO heterostructure forms a type-II band alignment with indirect band gap. Moreover, a red-shift (blue-shift) has been observed in SiS/GeC (SiS/ZnO) heterostructures as compared with the constituent monolayers, enhancing the efficient separation of photogenerated electron-hole pairs, thereby making them promising candidates for optoelectronic applications and solar energy conversion. More interestingly, significant charge transfers at the interfaces of SiS-ZnO heterostructures, have improved the adsorption of H, and the Gibbs free energy ΔH* becomes close to zero, which is optimal for the hydrogen evolution reaction to produce hydrogen. The findings pave the path for the practical realization of these heterostructures for potential applications in photovoltaics and photocatalysis of water splitting.

Theoretical prediction of a type-II BP/SiH heterostructure for high-efficiency electronic devices.

The generation of layered heterostructures from a combination of two or more different two-dimensional (2D) materials is considered as a powerful strategy to modify the electronic properties of 2D materials and enhance their performance in devices. Herein, using first-principles calculations, we systematically study the electronic properties and the band alignment in a heterostructure formed from 2D boron phosphide (BP) and silicane (SiH) monolayers. The BP/SiH heterostructure is structurally and mechanically stable in the ground state. The generation of the BP/SiH heterostructure leads to a reduction in the band gap, thus enhancing the optical absorption coefficient compared to the constituent BP and SiH monolayers. In addition, the BP/SiH heterostructure has a high carrier mobility of 3.2 × 104 cm2 V-1 s-1. Furthermore, the combined BP/SiH heterostructure gives rise to the formation of a type-II band alignment, inhibiting the recombination of the photogenerated carriers. The electronic properties and band alignment of the BP/SiH heterostructure can be tuned by an applied external electric field, which causes a reduction in the band gap and leads to the transition of the band alignment from type-II to type-I. Our findings could act as theoretical guidance for the use of the BP/SiH heterostructure in the design of high-efficiency nanodevices.

Tunability of the electronic properties and electrical contact in graphene/SiH heterostructures.

Stacking different two-dimensional materials to generate a vertical heterostructure has been considered a promising way to obtain the desired properties and improve device performance. Here, in this work, using first principles calculations, we design a vertical heterostructure by stacking graphene (GR) and silicane (SiH) and investigate the electronic properties and electrical contact in the GR/SiH heterostructure as well as the possibility of tuning these properties under an external electric field and vertical strain. The GR/SiH heterostructure is structurally and mechanically stable at the equilibrium interlayer separation. The GR/SiH heterostructure exhibits a p-type Schottky contact with a small Schottky barrier of 0.43 eV, presenting great tunability of the electrical contact from Schottky to Ohmic contact under different conditions. The external electric field not only leads to a transition from the p-type to n-type Schottky contact but also induces a transformation from a Schottky contact to Ohmic one. Furthermore, changing the interlayer separation can be considered a useful tool to regulate the Schottky barriers and electric contact in the GR/SiH heterostructure, which is prominent for constructing electronic devices. Our findings could provide an effective tool for the design of high-performance nanoelectronic devices based on the GR/SiH heterostructure.

First principles prediction of two-dimensional Janus XMoGeN2 (X = S, Se and Te) materials.

Motivated by the successful synthesis of two-dimensional MoSi2N4 [Y.-L. Hong et al., Science, 2020, 369, 670-674] and Janus MoSSe [A.-Y. Lu et al., Nat. Nanotechnol., 2017, 12, 744-749], in this work, we propose novel 2D Janus XMoGeN2 (X = S, Se and Te) monolayers using first-principles prediction. The controllable electronic features of Janus XMoGeN2 (X = S, Se and Te) monolayers under an external electric field and strain are also examined. Our predictions demonstrated that 2D XMoGeN2 materials are structurally and dynamically stable. All these 2D XMoGeN2 materials are indirect semiconductors with band gaps of 1.60/2.10, 1.54/2.07 and 1.05/1.56 eV obtained by the PBE/HSE functional for SMoGeN2, SeMoGeN2 and TeMoGeN2 monolayers, respectively. Furthermore, the electronic band gap and band structures of these monolayers are controllable under an external electric field and strain, making them promising candidates for flexible optoelectronics and nanoelectronics. The electric field tunes the TeMoGeN2 monolayer from semiconductor to metal and leads to a change in the band gap. While strain modifies the band gap of the TeMoGeN2 monolayer, giving rise to a shift in the CB from the Γ-M path to the M point and a tendency to transform from semiconductor to metal. Our findings suggest that these novel 2D XMoGeN2 materials are potential candidates for use in future high-performance applications.

Electric field tunability of the electronic properties and contact types in the MoS2/SiH heterostructure.

The generation of layered heterostructures with type-II band alignment is considered to be an effective tool for the design and fabrication of a highly efficient photocatalyst. In this work, we design a novel type-II MoS2/SiH HTS and investigate its atomic structure, electronic properties and contact types. In the ground state, the MoS2/SiH HTS is proved to be structurally and mechanically stable. The MoS2/SiH HTS generates type-II band alignment with separation of the photogenerated carriers. Both the electronic properties and contact type of the MoS2/SiH HTS can be modulated by an external electric field. The application of a negative electric field leads to a transformation from type-II to type-I band alignment. While the application of a positive electric field gives rise to a transition from semiconductor to metal in the MoS2/SiH HTS. These results could provide useful information for the design and fabrication of photoelectric devices on the MoS2/SiH HTS.

Rashba-type spin splitting and transport properties of novel Janus XWGeN2 (X = O, S, Se, Te) monolayers.

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN2 (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN2 are predicted to be stable and they are all indirect semiconductors in the ground state. When the spin-orbit coupling (SOC) is included, a large spin splitting at the K point is found in XWGeN2 monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN2, SeWGeN2, and TeWGeN2. The Rashba parameters in these structures are directionally isotropic along the high-symmetry directions Γ-K and Γ-M and the Rashba constant αR increases as the X element moves from S to Te. TeWGeN2 has the largest Rashba energy up to 37.4 meV (36.6 meV) in the Γ-K (Γ-M) direction. Via the deformation potential method, we calculate the carrier mobility of all four XWGeN2 monolayers. It is found that the electron mobilities of OWGeN2 and SWGeN2 monolayers exceed 200 cm2 V-1 s-1, which are suitable for applications in nanoelectronic devices.

Intriguing interfacial characteristics of the CS contact with MX2 (M = Mo, W; X = S, Se, Te) and MXY ((X ≠ Y) = S, Se, Te) monolayers.

Using (hybrid) first principles calculations, the electronic band structure, type of Schottky contact and Schottky barrier height established at the interface of the most stable stacking patterns of the CS-MX2 (M = Mo, W; X = S, Se, Te) and CS-MXY ((X ≠ Y) = S, Se, Te) MS vdWH are investigated. The electronic band structures of CS-MX2 and CS-MXY MS vdWH seem to be simple sum of CS, MX2 and MXY monolayers. The projected electronic properties of the CS, MX2 and MXY layers are well preserved in CS-MX2 and CS-MXY MS vdWH. Their smaller effective mass (higher carrier mobility) render promising prospects of CS-WS2 and CS-MoSeTe as compared to other MS vdWH in nanoelectronic and optoelectronic devices, such as a high efficiency solar cell. In addition, we found that the effective mass of holes is higher than that of electrons, suggesting that these heterostructures can be utilized for hole/electron separation. Interestingly, the MS contact led to the formation of a Schottky contact or ohmic contact, therefore we have used the Schottky Mott rule to calculate the Schottky barrier height (SBH) of CS-MX2 (M = Mo, W; X = S, Se, Te) and CS-MXY ((X ≠ Y) = S, Se, Te) MS vdWH. It was found that CS-MX2 (M = Mo, W; X = S, Se, Te) and CS-MXY ((X ≠ Y) = S, Se, Te) (in both model-I and -II) MS vdWH form p-type Schottky contacts. These p-type Schottky contacts can be considered a promising building block for high-performance photoresponsive optoelectronic devices, p-type electronics, CS-based contacts, and for high-performance electronic devices.

Thermoelectric properties of doped graphene nanoribbons: density functional theory calculations and electrical transport.

We present a detailed study on band structure-dependent properties such as electrical conductivity, the charge of carriers and Seebeck coefficients of graphene nano-ribbons (GNRs) doped with the magnetic impurities Fe and Co since the spin thermopower could be considerably enhanced by impurities. Thermoelectric properties of two-dimensional systems are currently of great interest due to the possibility of heat to electrical energy conversion at the nanoscale. The thermoelectric properties are investigated using the semi-classical Boltzmann method. The electronic band structure of doped nano-ribbons is evaluated by means of density-functional theory in which the Hubbard interaction is considered. Different types of nano-ribbons (armchair-edge and zigzag-edge) and their thermoelectric features such as conductivity and Seebeck coefficient in the presence and absence of magnetic impurities have been studied.

Two-Dimensional Metal/Semiconductor Contact in a Janus MoSH/MoSi2N4 van der Waals Heterostructure.

Following the successful synthesis of single-layer metallic Janus MoSH and semiconducting MoSi2N4, we investigate the electronic and interfacial features of metal/semiconductor MoSH/MoSi2N4 van der Waals (vdW) contact. We find that the metal/semiconductor MoSH/MoSi2N4 contact forms p-type Schottky contact (p-ShC type) with small Schottky barrier (SB), suggesting that Janus MoSH can be considered as an efficient metallic contact to MoSi2N4 semiconductor with high charge injection efficiency. The electronic structure and interfacial features of the MoSH/MoSi2N4 vdW heterostructure are tunable under strain and electric fields, which give rise to the SB change and the conversion from p-ShC to n-ShC type and from ShC to Ohmic contact. These findings could provide a new pathway for the design of optoelectronic applications based on metal/semiconductor MoSH/MoSi2N4 vdW heterostructures.

Two-Dimensional Boron Phosphide/MoGe2N4 van der Waals Heterostructure: A Promising Tunable Optoelectronic Material.

A van der Waals (VDW) heterostructure offers an effective strategy to create designer physical properties in vertically stacked two-dimensional (2D) materials, and offers a new paradigm in designing novel 2D heterostructure devices. In this work, we investigate the structural and electronic features of the BP/MoGe2N4 heterostructure. We show that the BP/MoGe2N4 heterostructure exists in a multiple structurally stable stacking configuration, thus revealing the experimental feasibility of fabricating such heterostructures. Electronically, the BP/MoGe2N4 heterostructure is a direct band gap semiconductor exhibiting type-II band alignment, which is highly beneficial for the spatial separation of electrons and holes. Upon forming the BP/MoGe2N4 heterostructure, the band gap of the constituent BP and MoGe2N4 monolayers are substantially reduced, thus allowing the easier creation of an electron-hole pair at a lower excitation energy. Interestingly, both the band gap and band alignment of the BP/MoGe2N4 heterostructure can be modulated by an external electric field and a vertical strain. The optical absorption of the BP/MoGe2N4 heterostructure is enhanced in both the visible-light and ultraviolet regions, thus suggesting a strong potential for solar cell application. Our findings reveal the promising potential of the BP/MoGe2N4 vdW heterostructure in high-performance optoelectronic device applications.

Interfacial Electronic Properties and Tunable Contact Types in Graphene/Janus MoGeSiN4 Heterostructures.

Two-dimensional MoSi2N4 is an emerging class of 2D MA2N4 family, which has recently been synthesized in experiment. Herein, we construct ultrathin van der Waals heterostructures between graphene and a new 2D Janus MoGeSiN4 material and investigate their interfacial electronic properties and tunable Schottky barriers and contact types using first-principles calculations. The GR/MoGeSiN4 vdWHs are expected to be energetically favorable and stable. The high carrier mobility in graphene/MoGeSiN4 vdWHs makes them suitable for high-speed nanoelectronic devices. Furthermore, depending on the stacking patterns, either an n-type or a p-type Schottky contact is formed at the GR/MoGeSiN4 interface. The strain engineering and electric field can lead to the transformation from an n-type to a p-type Schottky contact or from Schottky to Ohmic contact in graphene/MoGeSiN4 heterostructure. These findings provide useful guidance for designing controllable Schottky nanodevices based on graphene/MoGeSiN4 heterostructures with high-performance.

Electronic, optical, and thermoelectric properties of Janus In-based monochalcogenides.

Inspired by the successfully experimental synthesis of Janus structures recently, we systematically study the electronic, optical, and electronic transport properties of Janus monolayers In2XY(X/Y= S, Se, Te withX≠Y) in the presence of a biaxial strain and electric field using density functional theory. Monolayers In2XYare dynamically and thermally stable at room temperature. At equilibrium, both In2STe and In2SeTe are direct semiconductors while In2SSe exhibits an indirect semiconducting behavior. The strain significantly alters the electronic structure of In2XYand their photocatalytic activity. Besides, the indirect-direct gap transitions can be found due to applied strain. The effect of the electric field on optical properties of In2XYis negligible. Meanwhile, the optical absorbance intensity of the Janus In2XYmonolayers is remarkably increased by compressive strain. Also, In2XYmonolayers exhibit very low lattice thermal conductivities resulting in a high figure of meritZT, which makes them potential candidates for room-temperature thermoelectric materials.