N-type Schottky Contact Research Articles

Tunable interfacial properties of monolayer GeSb2Te4 on metal surfaces

Abstract Atomically thin monolayer (ML) GeSb 2 Te 4 (GST) holds promising prospects in non-volatile memory applications because of its high non-homogeneous crystallization rate. In GST-based devices, the interaction between GST and metals is crucial, as it affects the electronic properties. Herein, based on first-principles calculations, we investigate the interaction and Schottky barrier height of contacts formed by the combination of ML GST with various metals. It is found that the interfaces of GST with Pt, Pd, Ir and W exhibit strong interaction, characterized by large binding energies ranging from 1.394 to 1.015 eV , and the interfaces between GST and Cu, Ag and Au display weak interaction. For the seven contacts, Ag and W form Ohmic contacts with ML GST, while Cu, Au, Pd, Ir, and Pt form n-type Schottky contacts, with Schottky barrier heights ranging from 0.029 to 0.353 eV . The strong Fermi level pinning at GST-metal interface is observed with a pinning factor of 0.378. Additionally, altering the interfacial distance and optimizing the layers of GST enable a transition from Ohmic contact to Schottky contact. These findings provide crucial guidance for the design and optimization of electronic devices based on phase change materials like GST.

Unveiling Versatile Electronic Properties and Contact Features of Metal-Semiconductor Graphene/γ-Ge2SSe van der Waals Heterostructures.

Recently, searching for a metal-semiconductor junction (MSJ) that exhibits low-contact resistance has received tremendous consideration, as they are essential components in next-generation field-effect transistors. In this work, we design a MSJ by integrating two-dimensional (2D) graphene as the metallic electrode and 2D Janus γ-Ge2SSe as the semiconducting channel using first-principles simulations. All the graphene/γ-Ge2SSe MSJs are predicted to be energetically, mechanically, and thermodynamically stable, characterized by the weak van der Waals (vdW) interactions. The graphene/γ-SGe2Se MSJ-vdWH form the n-type Schottky contact (SC), while the graphene/γ-SeGe2S MSJ-vdWH form the p-type one, suggesting that the switching between p-type and n-type SC in the graphene/γ-Ge2SSe MSJ-vdWHs can occur spontaneously by simply altering the stacking patterns, without requiring any external conditions. Notably, the contact features, including contact types and barriers of the graphene/γ-Ge2SSe MSJs are significant in versatility and can be altered by applying electric gating and adjusting interlayer spacing. Both the applied electric gating and strain engineering induce switchability between p- and n-type and SC to OC in the graphene/γ-Ge2SSE MSJs. This versatility underscores the potential of the graphene/γ-Ge2SSe MSJ for next-generation applications that require low-contact resistance and high performance.

Electrical contact property and control effects for stable T(H)-TaS2/C3B metal-semiconductor heterojunctions.

Metal-semiconductor heterojunctions are the basis for developing new electronic devices. Here, T(H)-TaS2/C3B metal-semiconductor heterostructures are constructed by different phase T- and H-TaS2 monolayers combined with the C3B monolayer. The calculated corrected binding energies, phonon band structures, elastic constants, and molecular dynamics simulations indicated that both heterojunctions are highly stable, meaning that T(H)-TaS2/C3B heterojunctions possibly exist in experiments. The electronic property calculations showed that the intrinsic T(H)-TaS2/C3B heterojunction is an n(p)-type Schottky contact with a low Schottky barrier height (SBH), which is very important for the design of high-performance field-effect transistors. The electronic properties of the T(H)-TaS2/C3B heterojunctions can be controlled by varying the vertical strain and external electric field; however, the strain only resulted in a small change in the heterojunction SBH. Nevertheless, under external electrical field control, the T-TaS2/C3B heterojunction could manage a transition from an n-type Schottky contact to an n-type Ohmic contact and the H-TaS2/C3B heterojunction could be altered from a p-type Schottky contact to a p-type Ohmic contact. These findings provide theoretical insights into the electronic and electrical contact properties of the T(H)-TaS2/C3B heterojunction, which could be beneficial for developing n-type MOS and p-type MOS transistors.

Electronic properties of InSe/CNT heterojunctions with the modulation of electric field and vacancy defects

We investigate van der Waals (vdW) heterojunctions by combining InSe and zigzag carbon nanotubes (CNT(n,0)) by first-principle calculations. When n ranges from 5 to 7, The heterojunctions show n-type Schottky contact. However, for n of 8, 9, and 11, the heterojunctions still retain the characteristic of semiconductors with bandgaps. The metallized InSe/CNT(10,0) heterojunction has the most amount of charge transfer and the highest tunneling probability. Ohmic contact can be formed in InSe/CNT(n,0) (n = 5–7) heterojunctions under the external electric field. The charge transfer is enhanced and Schottky barrier heights are significantly reduced in heterojunctions with Se vacancy defect. In vacancy defect causes the disappearance of Schottky barrier because of metallization of InSe and more charge transfer than Se vacancy defect in InSe/CNT. Our findings provide a direction for the application of InSe/CNT in tunable nanoelectronic devices.

Schottky-barrier-free contacts with Janus WSSe 2D semiconductor using surface-engineered MXenes

Forming low-barrier contacts at metal/semiconductor interfaces is an important research area. The Fermi level pinning (FLP) effect is induced by strong interactions between 3D metal/semiconductor interfaces. By using a 2D metal in contact with a 2D semiconductor, the FLP effect can be weakened considerably, resulting in a reduction of the Schottky barrier height (SBH). Surface-engineered MXenes are the best electrode materials available presently. Therefore, herein, the interfacial properties of surface-engineered MXenes (M2CT2) (M=Hf, Mo, Ta, Zr, Nb; T = F, OH, O)/Janus WSSe (WSSe) heterostructures are systematically investigated using first-principles calculations. OH-terminated MXenes [M2C(OH)2]/WSSe heterostructures are found to form n-type ohmic contacts, and the tunnelling probabilities are high. O-terminated MXenes (M2CO2)/WSSe heterostructures tend to form p-type ohmic contacts and p-type Schottky contacts with a very low SBH, and the tunnelling probability is low. Conversely, F-terminated MXenes (M2CF2)/WSSe heterostructures form n-type and p-type Schottky contacts readily and n-type ohmic contacts (Hf2CF2/WSSe and Zr2CF2/SWSe heterostructures) partially, and the tunnelling probability is found to be low. In addition, the synergistic action of interface and intrinsic dipoles can effectively tune the contact type and SBH of the M2CT2/WSSe heterostructures, transforming the Mo2CF2/WSSe and Nb2CF2/WSSe heterostructures from n-type to p-type Schottky contacts. Through this novel strategy, an SB-free contact can be readily obtained, especially for OH-terminated MXenes (which are the most ideal electrode materials), followed by O-terminated MXenes. This work provides an important reference for the selection of suitable electrode materials and a novel approach for the development of high-performance electronic devices based on Janus WSSe.

Contact engineering for two-dimensional metal/qHP C60 van der Waals heterostructure

The fabrication of two-dimensional (2D) quasi-hexagonal phase (qHP) C60 semiconductor material offers a promising candidate for high-performance electronic devices. Selecting appropriate metals is crucial for achieving Ohmic contact (OhC) to enhance carrier injection efficiency. In this Letter, we used first-principles calculations to study the contact properties of seven 2D metal/qHP C60 van der Waals heterostructures. Metals with suitable work functions can form p-type Schottky contacts (p-ShCs), n-type Schottky contacts (n-ShCs), and OhCs. Differences in work function affect interface charge transfer, creating interface dipoles and causing band alignment deviations from the ideal Schottky–Mott limit. The calculated Fermi level pinning factors for n-type and p-type 2D metal/qHP C60 vdWh are 0.528 and 0.521, respectively. By regulating Φn and Φp based on electrostatic potential difference ΔV, we have achieved the ideal Schottky–Mott limit. We also studied the Schottky barrier height of the germanene/qHP C60 vdWh, finding that using electric field is an effective way to convert n-ShC to OhC or p-ShC. These findings provide theoretical guidance for constructing efficient 2D qHP C60 electronic devices.

P-Type Schottky Contacts for Graphene Adjustable-Barrier Phototransistors.

The graphene adjustable-barriers phototransistor is an attractive novel device for potential high speed and high responsivity dual-band photodetection. In this device, graphene is embedded between the semiconductors silicon and germanium. Both n-type and p-type Schottky contacts between graphene and the semiconductors are required for this device. While n-type Schottky contacts are widely investigated, reports about p-type Schottky contacts between graphene and the two involved semiconductors are scarce. In this study, we demonstrate a p-type Schottky contact between graphene and p-germanium. A clear rectification with on-off ratios of close to 103 (±5 V) and a distinct photoresponse at telecommunication wavelengths in the infrared are achieved. Further, p-type silicon is transferred to or deposited on graphene, and we also observe rectification and photoresponse in the visible range for some of these p-type Schottky junctions. These results are an important step toward the realization of functional graphene adjustable-barrier phototransistors.

First-Principles Study of the Schottky Contact, Tunneling Probability, and Optical Properties of MX/TiB4 Heterojunctions (M = Ge, Sn; X = S, Se, Te): Strain Engineering Tunability.

Designing two-dimensional (2D) heterojunctions with rapid response and minimal energy consumption holds immense significance for the advancement of the next generation of electronic devices. Here, we construct a series of Schottky heterojunctions based on TiB4 monolayer and group-IV monochalcogenide monolayers MX (M = Ge, Sn; X = S, Se, Te). Using first-principles calculations, we investigate the structural stability, Schottky contact barrier, tunneling probability, and optical properties of MX/TiB4 heterojunctions. The calculated binding energies reveal that X-type MX/TiB4 heterojunctions exhibit more stable structures than M- and C-type stacking modes. Schottky barrier heights (SBHs) indicate that X-type GeSe/TiB4 and GeTe/TiB4 form n-type Schottky contacts with SBHs of 0.497 and 0.132 eV, respectively, while SnS/TiB4 and SnSe/TiB4 form p-type Schottky contacts with SBHs of 0.557 and 0.418 eV, respectively. Moreover, X-type MX/TiB4 heterojunctions exhibit high susceptibility to interlayer electron tunneling due to their large tunneling probability and strong interlayer interaction. Meanwhile, enhanced optical absorption capacity in MX/TiB4 heterojunctions is also observed compared with individual TiB4 and MX monolayers. By applying in-plane biaxial strain, the transformation of MX/TiB4 heterojunctions from a Schottky contact to an Ohmic contact can also be realized. Our findings could offer valuable candidate materials and guidance for the design of the next generation of nanodevices with high electronic and optical performances.

Strong hybridization of Nb2C with MoS2: a way to reduce contact resistance

The hybridization of MXene materials and transition metal dichalcogenides has a significant impact on heterojunction properties. The transport properties and electronic structure of heterojunctions of semiconducting MoS2 and metallic MXene Nb2C were studied by integrating density functional theory with non-equilibrium Green’s function theory. The hybridization between Nb2C and MoS2 makes the tunneling barrier between the two layers disappear, which can enhance the electron injection efficiency from the Nb2C to the MoS2. Moreover, the Nb2C/MoS2 heterojunction exhibits a conventional n-type Schottky contact with a barrier height of 0.14 eV, which is significantly lower than the barrier height of 0.29 eV at the Ti/MoS2 junction. These factors result in a field-effect transistor with a low contact resistance of 138 Ω·μm and a higher current of 1.09 mA μm−1 at a bias voltage of 0.3 V applied between the left and right electrodes. Following the application of gate voltage, the I on/I off ratio reaches 1266.

High-performance Schottky-barrier field-effect transistors based on two-dimensional GaN with Ag or Au contacts

The performance of two-dimensional (2D) monolayer GaN Schottky barrier field effect transistors (SBFETs) with four different metals (Ag, Au, Al, and Pt) as electrodes were studied by using ab initio simulations. The N-type Schottky contact is formed on Ag-GaN, Au-GaN, and Pt-GaN, characterized by electron Schottky barrier heights (SBH) of 0.6, 0.5, and 0.38 eV, respectively. Whereas, Al-GaN contact formed P-type Schottky contact with hole SBH of 1.42 eV. The 5.1 nm GaN SBFETs with four metal electrodes all could overcome the short-channel effect. Additionally, GaN SBFETs with Ag and Au electrodes have excellent performance, whose ON-currents are 1151.1 μA/μm and 1258.9 μA/μm, respectively. They could satisfy the demands of International Technology Roadmap for Semiconductors for high-performance transistor. Furthermore, research indicates that the device's current increases with increasing temperature. Notably, under the constant bias and gate voltage, the current is unaffected by temperature variations between the left and right electrodes.

Unveiling the electronic properties of BiP[formula omitted] triphosphide from bulk to graphene-based heterostructures by first-principles calculations

In our study, we investigated the structural and electronic properties of bismuth triphosphide (BiP3) in its bulk, few-layer, and monolayer forms. We found that BiP3 in bulk exhibits a metallic stable layered structure. The exfoliation energy of 1.07 J/m2 indicates ease exfoliation, comparable to other triphosphides. The band gap varies with thickness, transitioning from semiconductor–metal between four to five layers, influenced by interlayer coupling and quantum confinement. We also investigated the heterostructure created by depositing graphene (G) on few-layer BiP3. In monolayer (G/m-BiP3) and bilayer (G/2L-BiP3) forms, a metal–semiconductor junction is formed, characterized by weak vdW interactions at the interface and exhibiting p-type Schottky contacts. We observed that the Schottky Barrier Height (SBH) can be modulated by altering the interlayer distance between G and BiP3. This adjustment allows transitions between n-type and p-type Schottky contacts in G/m-BiP3 and the formation of an ohmic contact in G/2L-BiP3. Furthermore, applying an electric field affects the SBH, leading to similar transitions and the development of an ohmic contact. Additionally, our study shows that n-doping in graphene increases with the number of BiP3 layers and external electric field application. These properties position BiP3 few-layer as a promising material for nanoelectronic, optoelectronic, and graphene-based devices.

Electric-field-controlled Schottky barriers in BSe/M2CF2 (M = Ta, W) van der Waals heterostructures: A computational study

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is regarded as an effective strategy to explore novel properties and enhance the performance of 2D materials. Herein, taking full advantage of boron selenide (BSe) and MXenes, 2D BSe/MXene vdW heterostructures are designed and their electronic and interfacial properties are investigated via first-principles calculations, by using BSe/Ta2CF2 and BSe/W2CF2 as models. The band structures of the BSe and M2CF2 (M = Ta, W) layers in the BSe/M2CF2 heterostructures are preserved quite well due to the weak vdW interlayer interaction. The Fermi level shifts towards the conduction band minimum of the BSe layer, leading to an n-type Schottky contact. Interestingly, the interface charge redistribution in BSe/W2CF2 is more pronounced compared to BSe/Ta2CF2, which can be attributed to the disparity in electronegativity between Ta and W. In particular, the Schottky barrier heights of both heterostructures vary linearly with the vertical electric field within a certain range. This allows for the tuning of the Schottky contact from n-type to p-type. However, the variation rate in BSe/W2CF2 is comparatively lower than that in BSe/Ta2CF2. Moreover, when the positive electric field exceeds 1.0 V/Å, a transition from the Schottky contact to the Ohmic contact in BSe/W2CF2 occurs, whereas the contact remains the Schottky contact in BSe/W2CF2. This work offers valuable insights into developing electronic nano-devices with tunable Schottky barriers using vdW heterostructures.

Schottky diodes based on in-plane TaSi2N4–WGe2N4 and TaSi2N4–MoGe2N4 heterojunctions

Ideal metal–semiconductor interfaces in 2D lateral heterojunctions are important to realize high-performance Schottky diodes. Based on the first-principles calculations, we propose in-plane heterojunction diodes composed of the metallic TaSi2N4 and the semiconductive WGe2N4/MoGe2N4 monolayers with extremely low lattice mismatch and nearly free defect states. N-type Schottky contacts are confirmed in both TaSi2N4–WGe2N4 and TaSi2N4–MoGe2N4 heterojunctions by analyzing the energy band alignment, charge transfer, electrostatic differential potential, and effective potential. Then, the volt-ampere characteristics and the rectification effect of heterojunctions are investigated. An ultrahigh rectification ratio of 106/107 is obtained for the TaSi2N4–WGe2N4/MoGe2N4 heterojunction diode via regulating the length of the semiconductor part of the heterojunctions. The regulatory mechanism is elucidated by the asymmetrical evolutions of transmission spectra within positive and negative energy ranges. Finally, the rectification mechanism is revealed by the local density of states and the potential energy drop under bias voltages. These results provide a guideline for designing in-plane heterojunction diodes with ultrahigh rectification.

Interfacial Properties of Anisotropic Monolayer SiAs Transistors

The newly prepared monolayer (ML) SiAs is expected to be a candidate channel material for next-generation nano-electronic devices in virtue of its proper bandgap, high carrier mobility, and anisotropic properties. The interfacial properties in ML SiAs field-effect transistors are comprehensively studied with electrodes (graphene, V2CO2, Au, Ag, and Cu) by using ab initio electronic structure calculations and quantum transport simulation. It is found that ML SiAs forms a weak van der Waals interaction with graphene and V2CO2, while it forms a strong interaction with bulk metals (Au, Ag, and Cu). Although ML SiAs has strong anisotropy, it is not reflected in the contact property. Based on the quantum transport simulation, ML SiAs forms n-type lateral Schottky contact with Au, Ag, and Cu electrodes with the Schottky barrier height (SBH) of 0.28 (0.27), 0.40 (0.47), and 0.45 (0.33) eV along the a (b) direction, respectively, while it forms p-type lateral Schottky contact with a graphene electrode with a SBH of 0.34 (0.28) eV. Fortunately, ML SiAs forms an ideal Ohmic contact with the V2CO2 electrode. This study not only gives a deep understanding of the interfacial properties of ML SiAs with electrodes but also provides a guide for the design of ML SiAs devices.

Electronic properties, interface contact and transport properties of strain-modulated MS2/borophosphene and MSeS/borophosphene (M = Cr, Mo, W) heterostructure: Insights from first-principles

Controlling the interface contact performance to form low-resistance ohmic contact is of great importance in designing low-power two-dimensional (2D) devices. Here, we explore a 2D semi-metal with Dirac cones, borophosphene, for different types of contact with MS2, MSeS/borophosphene (M = Cr, Mo, W) using density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. The results indicate that under no strain, different van der Waals heterojunctions (vdWHs) exhibit an n-type (p-type) Schottky contact type, with the CrS2/borophosphene vdWHs exhibiting a lower barrier height (Φn = 0.08 eV). Next, we find that the in-plane strain is more efficient than the vertical strain. Under in-plane strain modulation, the contact type will change from Schottky to Ohmic contacts as the tensile strain increases. Similarly, the contact type will change from Schottky to semiconductor as the compressive strain increases. Under the influence of vertical strain, the CrS2/borophosphene vdWHs transition into ohmic contact only when the interlayer spacing increases to above 0.4 Å. Finally, we study the ohmic contact formation and transport characteristics based on the device angle. These findings demonstrate that interface contact types can be effectively regulated by strain, which is crucial for the design and manufacturing of novel nano electronic devices composed of borophosphene based vdWHs.

First-principles studies on the electronic and contact properties of monolayer Ga2STe-metal contacts.

Monolayer (ML) Janus III-VI compounds have attracted the use of multiple competitive platforms for future-generation functional electronics, including non-volatile memories, field effect transistors, and sensors. In this work, the electronic and interfacial properties of ML Ga2STe-metal (Au, Ag, Cu, and Al) contacts are systematically investigated using first-principles calculations combined with the non-equilibrium Green's function method. The ML Ga2STe-Au/Ag/Al contacts exhibit weak electronic orbital hybridization at the interface, while the ML Ga2STe-Cu contact exhibits strong electronic orbital hybridization. The Te surface is more conducive to electron injection than the S surface in ML Ga2STe-metal contact. Quantum transport calculations revealed that when the Te side of the ML Ga2STe is in contact with Au, Ag and Cu electrodes, p-type Schottky contacts are formed. When in contact with the Al electrode, an n-type Schottky contact is formed with an electron SBH of 0.079 eV. When the S side of ML Ga2STe is in contact with Au and Al electrodes, p-type Schottky contacts are formed, and when it is in contact with Ag and Cu electrodes, n-type Schottky contacts are formed. Our study will guide the selection of appropriate metal electrodes for constructing ML Ga2STe devices.

Self-formed asymmetric Schottky contacts between graphene and WSiGeN4.

In this paper, the electronic properties and transport characteristics of WSiGeN4/graphene heterostructures were explored by combining the quantum transport method with first-principle calculations. The band structures indicate that the heterostructures can form either p-type or n-type Schottky contacts, depending on the stacking mode. Due to the self-formed asymmetric Schottky contacts, we design an asymmetric van der Waals (vdW) metal-semiconductor-metal (MSM) structure, which exhibits a pronounced asymmetric current-voltage (I-V) curve. The corresponding physical mechanisms are attributed to carrier transport mechanisms, which are primarily governed by thermionic excitation at positive bias voltages and tunneling effects at negative bias voltages. Our study offers a viable strategy for integrating asymmetric Schottky barriers into MSM configurations, laying the groundwork for a wider range of applications in a range of Janus two-dimensional semiconductors.

Contact evaluation of the penta-PdPSe/graphene vdW heterojunction: tuning the Schottky barrier and optical properties.

In this work, we design a van der Waals heterojunction composed of semiconducting penta-PdPSe and semi-metallic graphene (G) monolayers based on state-of-the-art theoretical calculations. Our results show that both monolayers well preserve their intrinsic features and possess an n-type near Ohmic Schottky contact with a low Schottky barrier height of 0.085 eV for the electrons at the vertical interface. The electronic band alignment suggests a negative band bending of -1.47 eV at the lateral interface, implying electrons as the major transport carriers. Moreover, the transmission gap closely mirrors the heterojunction's band gap, indicating a subtle yet profound interaction between graphene and penta-PdPSe monolayers, which leads to enhanced optical absorption coefficient reaching 106 cm-1 and strong conductivity spanning the visible to ultraviolet region. In addition, our study demonstrates the ability to modify the penta-PdPSe/G heterojunction interface, switching between p-type as well as Ohmic contacts by applying external electric fields. These properties render the penta-PdPSe/G heterojunction promising for optoelectronic applications.

Ohmic contact in two-dimensional WS2/Hf2CX2 (X = F/OH) and WS2/graphene/Hf2C heterojunctions

Low-resistance Ohmic contacts are the key to improving the performance of electronic devices. By performing ab initio electronic calculations and quantum transport simulations, we systematically investigate the contact types of the original WS2/Hf2C, the functionalized WS2/Hf2CX2 (X = F/OH), and the graphene-doped WS2/graphene/Hf2C heterojunctions. The obtained results suggest that the strong interfacial coupling occurs in the WS2/Hf2C system, leading to the metallization of the WS2 layer. Functionalization of the Hf2C layer can significantly weaken the interlayer interactions. Thus, the semiconductor characteristics of the WS2 layer can be maintained in the WS2/Hf2CX2 (X = F/OH) and WS2/graphene/Hf2C heterojunctions. Stable Ohmic contacts are formed in these heterojunctions. The heights of the vertical electron Schottky barrier are −0.13 eV, −0.43 eV, and −0.12 eV for WS2/Hf2CF2, WS2/Hf2C(OH)2, and WS2/graphene/Hf2C, respectively. Based on these heterojunctions, we construct a two-probe field-effect transistor model and explore its quantum transport properties. In the lateral direction, all systems form n-type Schottky contacts. This investigation provides a basis for the selection of electrode materials based on WS2 devices.

Electronic and optical properties of MoSSe/borophene heterojunctions with the modulation of electric field and vacancy defects

We investigate the electronic and optical properties of MoSSe/borophene heterojunctions by first principles. Two different structures of borophene and several different stacking layers are considered. The heterojunctions of SeMoS/H, SMoSe/H, and SMoSe/β exhibit the p-type Schottky contacts, while SeMoS/β presents a n-type Schottky contact. When the external electric field is applied to heterojunctions, the Ohmic contact is achieved for SeMoS/H and SMoSe/H. The introduction of S and Se vacancy defects reduces the Schottky barrier height. The heterojunctions of SeMoS/H-VS and SMoSe/H-VS exhibit the Ohmic contact. Moreover, the optical absorption of heterojunctions with vacancy defects has been significantly enhanced, and SeMoS/β-VS has the maximum optical absorption coefficient of 2.35 × 104 cm−1. Our results can provide some guidance for the widespread application of two-dimensional heterostructures in tunable nanoelectronics devices.