Work Function Of Metal Electrode Research Articles

Formation and energetics of head-to-head and tail-to-tail domain walls in hafnium zirconium oxide

180∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document} domains walls (DWs) of head-to-head/tail-to-tail (H–H/T–T) type in ferroelectric (FE) materials are of immense interest for a comprehensive understanding of the FE attributes as well as harnessing them for new applications. Our first principles calculation suggests that such DW formation in hafnium zirconium oxide (HZO) based FEs depends on the unique attributes of the HZO unit cell, such as polar-spacer segmentation. Cross pattern of the polar and spacer segments in two neighboring domains along the polarization direction (where polar segment of one domain aligns with the spacer segment of another) boosts the stability of such DWs. We further show that low density of oxygen vacancies at the metal-HZO interface and high work function of metal electrodes are conducive for T–T DW formation. On the other hand, high density of oxygen vacancy and low work function of metal electrode favor H–H DW formation. Polarization bound charges at the DW get screened when band bending from depolarization field accumulates holes (electrons) in T–T (H–H) DW. For a comprehensive understanding, we also investigate their FE nature and domain growth mechanism. Our analysis suggests that a minimum thickness criterion of domains has to be satisfied for the stability of H–H/T–T DW and switching of the domains through such DW formation.

SCAPS-1D Simulation for Device Optimization to Improve Efficiency in Lead-Free CsSnI3 Perovskite Solar Cells

In this study, a novel systematic analysis was conducted to explore the impact of various parameters, including acceptor density (NA), individual layer thickness, defect density, interface defect density, and the metal electrode work function, on efficiency within the FTO/ZnO/CsSnI3/NiOx/Au perovskite solar cell structure through the SCAPS-1D (Solar Cell Capacitance Simulator in 1 Dimension) simulation. ZnO served as the electron transport layer (ETL), CsSnI3 as the perovskite absorption layer (PAL), and NiOx as the hole transport layer (HTL), all contributing to the optimization of device performance. To achieve the optimal power conversion efficiency (PCE), we determined the ideal PAL acceptor density (NA) to be 2 × 1019 cm−3 and the optimal thicknesses to be 20 nm for the ETL (ZnO), 700 nm for the PAL (CsSnI3), and 10 nm for the HTL (NiOx), with the metal electrode remaining as Au. As a result of the optimization process, efficiency increased from 11.89% to 23.84%. These results are expected to contribute to the performance enhancement of eco-friendly, lead-free inorganic hybrid solar cells with Sn-based perovskite as the PAL.

Influence of charge traps on charge plasma-germanium double-gate TFET for RF/Analog & low-power switching applications

The device reliability on account of charge traps at the Al2O3/Ge interface is a main distress for the Ge-based Tunnel Field Effect Transistor (TFET). Here, the influence of Interface Trap Charges (ITC) on the charge plasma-based Ge-Double-Gate TFET (CP-Ge-DGTFET) and conventional Ge-DGTFET's DC, Analog/RF, and linearity characteristics have been inspected using technology-computer-aided-design (TCAD) simulations for the donor (positive) and acceptor (negative) ITC. The charge plasma concept is adopted to induce excess carrier concentration within the source region on the integration of optimum work function metal electrodes. To recognize the impact of ITC, several figures of merits have been investigated, such as transfer characteristics, electric field, transconductance, cut-off frequency, parasitic capacitance, and linearity performance parameters (VIP2, VIP3, IIP3, and IMD3). The CP-Ge-DGTFET device structure revealed superior performance and reliability in comparison to Ge-DGTFET, even under the influence of ITC at the Al2O3/Ge interface. Therefore, the CP-Ge-DGTFET device structure is a sturdy contender for Analog/RF and low-power switching applications.

Optimal design of Cs<sub>2</sub>AgBi<sub>0.75</sub>Sb<sub>0.25</sub>Br<sub>6</sub> perovskite solar cells

Double perovskite solar cells have attracted much attention due to their low cost, high performance, environmental friendliness, and strong stability. In this study, the effect of thickness of perovskite layer, band offset, metal electrode work function, the thickness and doping concentration of the transport layer on the efficiency of Cs<sub>2</sub>AgBi<sub>0.75</sub>Sb<sub>0.25</sub>Br<sub>6</sub> solar cells are analyzed by using Silvaco TCAD to improve device performance. This preliminary study of device based on Spiro-OMeTAD as hole transport layer (HTL) and ZnO as electron transport layer (ETL) shows that the photovoltaic conversion efficiency (PCE) is 12.66%. The results show that the efficiency gradually saturates when the thickness of the perovskite layer is greater than 500 nm. The optimal conduction band offset (CBO) ranges from 0 eV to +0.5 eV and the optimal valence band offset (VBO) from –0.1 eV to +0.2 eV. After changing the device's ETL into ZnOS and HTLs into MoO<sub>3</sub>, Cu<sub>2</sub>O and CuSCN, respectively, and optimizing their thickness values and doping concentrations, the final theoretical photovoltaic conversion efficiency of the double perovskite solar cell with an HTL of Cu<sub>2</sub>O can reach 22.85%, which is increased by 25.6% compared with the currently reported theoretical efficiency value. Moreover, the optimal efficiency is achieved when the metal electrode work function is less than –4.9 eV. This work will help find suitable materials for the transport layer and provide guidance for developing the high-performance and lead-free perovskite solar cells.

Optimal design of Cs<sub>2</sub>AgBi<sub>0.75</sub>Sb<sub>0.25</sub>Br<sub>6</sub> perovskite solar cells

Double perovskite solar cells have attracted much attention due to their low cost, high performance, environmental friendliness, and strong stability. In this study, the effect of thickness of perovskite layer, band offset, metal electrode work function, the thickness and doping concentration of the transport layer on the efficiency of Cs<sub>2</sub>AgBi<sub>0.75</sub>Sb<sub>0.25</sub>Br<sub>6</sub> solar cells are analyzed by using Silvaco TCAD to improve device performance. This preliminary study of device based on Spiro-OMeTAD as hole transport layer (HTL) and ZnO as electron transport layer (ETL) shows that the photovoltaic conversion efficiency (PCE) is 12.66%. The results show that the efficiency gradually saturates when the thickness of the perovskite layer is greater than 500 nm. The optimal conduction band offset (CBO) ranges from 0 eV to +0.5 eV and the optimal valence band offset (VBO) from –0.1 eV to +0.2 eV. After changing the device's ETL into ZnOS and HTLs into MoO<sub>3</sub>, Cu<sub>2</sub>O and CuSCN, respectively, and optimizing their thickness values and doping concentrations, the final theoretical photovoltaic conversion efficiency of the double perovskite solar cell with an HTL of Cu<sub>2</sub>O can reach 22.85%, which is increased by 25.6% compared with the currently reported theoretical efficiency value. Moreover, the optimal efficiency is achieved when the metal electrode work function is less than -4.9 eV. This work will help find suitable materials for the transport layer and provide guidance for developing the high-performance and lead-free perovskite solar cells.

Simulation of MASnI3-based inverted perovskite solar cells with double hole transport layers and an electron transport layer

A model of CH3NH3SnI3 (MASnI3)-based inverted perovskite solar cell (PSC) with double hole transport layers (HTLs) and an electron transport layer (ETL) was established, and the device was studied using solar capacitance simulator (SCAPS). Compared with a single HTL, the double HTLs of CuI/MoO3 can improve device performance significantly. Among six ETLs, WS2 has been found to be the best ETL. Then, the effects of absorber layer thickness, CuI/MoO3 thickness, the defect density and doping density of the absorption layer, and metal electrode work function on device performance have been investigated in detail. According to the simulation results, the optimum thickness of MASnI3 is 500 nm, and the both CuI and MoO3 layers should be as thick as 20 nm. To achieve the ideal efficiency, the defect density of the absorption layer should be as low as 1 × 1014 cm−3, and its doping density should be 1 × 1016 cm−3. Moreover, the metal work function should be less than 4.42 eV to avoid the formation of a Schottky barrier at the WS2/metal interface. After optimization, the device can reach the highest efficiency of 28.13%. Our simulation results will help advance the manufacturing of high-performance Pb-free perovskite solar cells in the future.

Batch-Reproducible and Thickness-Insensitive Mesopolymer Zwitterion Interlayers for Organic Solar Cells

Zwitterionic polymers or small molecules are a class of widely used interlayer materials in organic solar cells (OSCs). It is challenging to develop such materials that combine good film-forming property, high batch-to-batch reproducibility, and broad thickness processing window in device applications. Herein, we designed and synthesized two self-doped conjugated mesopolymer zwitterions (CMZs), namely, MT2PDIMz and MT2PDINz (PDI = perylene-diimide, M = mesopolymer, T2 = dithiophene, Mz = imidazolium zwitterion, Nz = ammonium zwitterion). Both show good processability and effectively reduce the work function of metal electrodes. The substitution of imidazolium cations with ammonium cations on the side-chains can further modulate the solution assembly and self-doping effect of CMZs, enabling improved interfacial compatibility with active layers and higher electron mobility in MT2PDIMz. The versatility of CMZs interlayers for OSCs is confirmed with several binary and ternary active layers, affording efficiencies up to 19.01%. Notably, over 98% of the optimal efficiency is maintained as the thickness of the interlayers increases to 40 nm with good reproducibility.

Theoretical analysis of all-inorganic solar cells based on numerical simulation of CsGeI3/CsPbI3 with p-p+ built-in electric field

With the development of perovskite solar cells (PSCs) technology, inorganic perovskite led by CsPbI3 gradually shows the photovoltaic performance of organic perovskite cells. However, this is still based on the organic charge transport layer. CsPbI3 with all-inorganic structure still need to be further studied. Therefore, in this study, an all inorganic CsGeI3/CsPbI3 laminated structure with CsGeI3 instead of organic HTL is introduced, and numerical simulation is carried out through SCAPS-1D (Solar Cells Capability Simulator). It is found that the two perovskite layers, which are both p-type materials, have shown excellent efficiency in the p-p+ built-in electric field. In this paper, PSCs are optimized with absorbing layer thickness, doping concentration, defect density, metal electrode work function and so on. The best thickness is determined according to the different light absorption properties of Pb2+ and Ge2+, and the toxicity of the original single-layer lead based perovskite is reduced. Through the comprehensive analysis of band bending, built-in electric field and recombination rate, we explained the reason why the parameters increase with the growth of doping concentration (NA). In terms of NA regulation, it is found through simulation that when NA of the two absorption layers is at 1015 to 1018 cm−3, the photogenerated carriers are driven by the strong p-p+ built-in electric field to migrate well in the flat energy band, which significantly improves the photovoltaic performance of PSCs. For the defect density the charge transport layer, the PSC absorption characteristics, and the metal electrodes, we made a choice based on the photovoltaic performance and process level. Finally, the power conversion efficiency of the optimized PSCs reached 24.06 % and the fill factor is 86.19 %. This study proved that p-p+ structure constructed by lead germanium mixed metal has great potential for inorganic perovskite solar cells with Cs as a cation in the future.

Numerical simulation and performance optimization of GeSe based thin film solar cell with NiO as back surface field layer

Germanium monoselenide (GeSe) has emerged as a viable candidate for absorber material in thin film solar cell (TFSC) due to its favorable material characteristics. Herein, the novel GeSe based TFSC with CdS as buffer layer and NiO as back surface field (BSF) layer has been proposed and its photovoltaic performance has been evaluated theoretically using wxAMPS software. The device output parameters have been assessed by varying thickness and carrier concentration for the GeSe layer, CdS layer and NiO layer, respectively. Moreover, the defect densities in GeSe absorber layer, CdS/GeSe and GeSe/NiO interface layers, and the work function of metal electrode at the cell rear side have been altered to evaluate the photovoltaic characteristics. Conversion efficiency of 31.37% has been obtained for the proposed GeSe-based TFSC with the new architecture under the conditions such as the thicknesses of the CdS layer, GeSe layer and NiO layer are optimized to be 0.03 μm, 0.3 μm and 0.05 μm, respectively; the carrier concentrations of the CdS layer, GeSe layer and NiO layer are optimized to be 1018 cm−3, 1019 cm−3 and 1020 cm−3, respectively; the defect densities in the GeSe layer, IDL1, IDL2 both are set to be 1015 cm−3. These results suggest that GeSe can be employed as the promising absorber layer to fabricate low-cost and high efficiency TFSC.

Numerical investigation of the Cu2O solar cell with double electron transport layers and a hole transport layer

In this paper, a model of the Cu2O solar cell with double electron transport layers (ETLs) and a hole transport layer (HTL) has been investigated by SCAPS. Compared to the single ETL of ZnO, the problem of low open circuit voltage of the Cu2O solar cells can be improved by introducing the double ETLs of Zn(O,S)/ZnS. Our simulation results show that the sulfur concentration of Zn(O,S) and the donor density in double ETLs have a significant effect on device performance. The optimum S/S + O ratio and the best donor density are 0.82 and 8 × 1017cm−3, respectively. Due to the formation of an electron reflector and back surface field (BSF), an enhancement in both short circuit current density and open circuit voltage can be realized by introducing an appropriate HTL, and the best HTL is CuI, showing an efficiency of 12.15%. Then, the work function of metal electrode, the Cu2O thickness, the defect density and the acceptor density of Cu2O absorber layer, and the defect density at the Cu2O interfaces have been systematically investigated. After optimization, the best device efficiency of 16.49% can be achieved. Our results have demonstrated a new high-efficiency structure for cuprous oxide solar cells.

On the Role of Collective Electrostatic Effects in Electronic Level Pinning and Work Function Changes by Molecular Adlayers: The Case of Partially Fluorinated DNTTs Adsorbed Flat‐Lying on Various Metals and Hetero‐Structures

AbstractModifying the work function of metal electrodes by monolayers of molecules with specifically tailored electronic properties is a versatile tool, but such chemical modifications often also affect the adsorption geometry and packing density, making microscopic modeling difficult. Using scanning tunneling microscopy, it is shown that the recently synthesized partially fluorinated dinaphthothienothiophenes (DNTTs) adopt the same interface structure on different metal substrates independent of the degree of fluorination. Combining Kelvin probe measurements and density functional theory (DFT) calculations, a highest occupied molecular orbital (HOMO) pinning effect for such FxDNTTs on Au(111) and Ag(111) induced by collective electrostatic interactions in the monolayer is observed. Since the adsorption of weakly interacting molecules such as the FxDNTTs is not restricted to specific surfaces as is the case with SAMs, this concept is extended to metal substrates with quite different work function values. For a low work function surface such as Cs(110), a lowest unoccupied molecular orbital (LUMO) pinning effect is predicted at the theoretical level. Since such alkali metal surfaces are not experimentally accessible, a well‐defined Cs monolayer on Cu(100) as a low work function substrate is used instead. For this substrate, however, a variation is observed in the LUMO energies and the work function as a function of the degree of fluorination. This is attributed to the formation of a second interface dipole at the buried Cs/Cu interface, which is modulated with the degree of fluorination and competes with the dipole at the outer molecule/Cs interface. Such a second internal interface dipole, which can be modified by the top layer, has to be considered when going to more complex heterointerfaces.

Identifying the potentials for charge transport layers free n-p homojunction-based perovskite solar cells

Perovskite solar cells (PSCs) with no charge transport layers (CTLs) could be one of the major device architectures for the production of simple and low-cost devices. However, CTLs-free PSCs based on n-p homojunction have yet to show high power conversion efficiency (PCE), which is most likely due to inadequate light-and charge-management in the p-type perovskite. The device operation is examined using Solar Cell Capacitance Simulator (SCAPS)-software, and a novel n-p homojunction design is proposed to attempt efficient CTLs-free PSCs. Several aspects of p-type layer that can affect device performance, such as acceptor density, photon-harvesting capability, defects density, and resistances to the transport of charge-carriers are scrutinized and adjusted. Furthermore, the effects of different work-functions of metal electrodes are examined. A suitable acceptor concentration is required for oriented charge transport. It is determined that a p-type perovskite with a thickness of 0.3 μm is advantageous for high performance. A metal electrode with a high work-function is essential for efficient device. Consequently, a PCE of 15.60% is obtained with an optimal defect density of E15 cm−3, indicating that n-p homojunction-based CTLs-free PSCs are promising since they simplify the device design and fabrication process while retaining an acceptable PCE.

Performance analysis of different material based dual electrode doping-less TFET

In this work, the charge plasma based dual electrode doping-less tunnel FETs (DEDLTFET) is simulated with the use of different materials such as silicon (Si-DEDLTFET), Silicon-germanium (SiGe-DEDLTFET) and SiGe at Source (SiGe Source DEDLTFET). The charge plasma technique is used to create source and drain region on an intrinsic body by selecting appropriate work function of metal electrode. The paper provides the comparison among devices on the basis of RF parameters. The on-state current (ION) for SiGe source DEDLTFET, SiGe-DEDLTFET and DEDLTFET are 1.84x10-4, 8.75x10-5 and 8.11x10-6 A/µm respectively for similar off-state current (IOFF). This result show that SiGe source DEDLTFET device provides better drive current along with improved ON-OFF current ratio (ION/IOFF) and subthreshold slope (SS). Improved transconductance (gm) and cut-off frequency (fT) show that the hetero-material device has better RF performance while comparing with the other two devices. Copyright © 2017 VBRI Press.

Electrical Performance Enhanced Doping Less Tunnel Field Effect Transistor by Metal Electrode Work Function Engineering

Tunnel field effect transistor (TFET) has been proposed as one of the promising alternative devices to MOSFET since it has low power consumption and excellent subthreshold swing (SS) characteristics of less than 60 mV / dec. However, conventional TFET fabrication requires ion implantation process to form p-i-n structure in active region, which induces a random distribution of dopant atoms. In the nm-scale device, even a small number of dopant atom dispersion can cause electrical characteristic variations such as threshold voltage (Vt)1, so alternative method for forming p-i-n region instead of doping process is needed.Doping-less TFET (DL-TFET) introduces charge plasma concept2 that controls carrier concentration of Si region by band alignment in MOS contact not by doping process, so random dopant fluctuation (RDF) issue can be solved. Since the active region carrier concentration is determined by the work function of the metal electrode, it is necessary to analyze the device performance by the metal work function condition. In this work, we manufactured doping-less TFET with adapting various metal work function to enhance electrical performance, and conducted CV measurement in MOS structure to confirm Si band bending and charge plasma by analyzing flat band voltage (VFB).DL-TFET was fabricated on SOI wafer and the overall structure is shown in Fig. 1. (a). In the case of the source region, the metal work function must be larger than that of Si to form the p-type active area, and drain region, on the contrary, must have smaller work function for n-type active region. Obviously, gate electrode work function has similar work function to intrinsic Si. For fabricating DL-TFET, we conducted reactive ion etch (RIE) process to define Si active layer and formed gate oxide (SiO2) by thermal oxidation. Then, we deposited gate metal and removed source / drain region oxide for contact hole. Spacer oxide was deposited using PECVD to isolate each metal electrode, finally we deposited source / drain metal. IV characteristics are shown in Fig. 1. (b), (c) when Pt / W / Al is applied at source / gate / drain area and we compared IV curve of various metal electrode and thermal conditions.In addition, to confirm whether the charge plasma was formed as intended, we fabricated MOS capacitor with 10 nm oxide thickness as shown in Fig. 1. (d). Through frequency sweep, we determined suitable bias frequency and conducted CV measurement (see Fig. 1. (e), (f), (g)). Band bending and charge plasma were confirmed by evaluating VFB shift depending on work function of each MOS gate material (see Fig. 1. (h)). Finally, we discussed the optimal metal electrode combination in terms of ambipolar current, off current, on current and SS. Key Words: Charge plasma, Doping-less TFET, Work function, CV measurement References Changho Shin, Jeong-Kyu Kim, Gwang-Sik Kim, Hyunjae Lee, Changhwan Shin, Jong-Kook Kim, Byung Jin Cho, and Hyun-Yong Yu, “Random Dopant Fluctuation-Induced Threshold Voltage Variation-Immune Ge FinFET With Metal–Interlayer–Semiconductor Source/Drain,” IEEE TRANSACTIONS ON ELECTRON DEVICES, vol. 63, No. 11, pp 4167-4172, Nov 2016. doi: 10.1109/TED.2016.2606511 Raymond J. E. Hueting, Bijoy Rajasekharan, Cora Salm, and d Jurriaan Schmitz, " The Charge Plasma P-N Diode" IEEE ELECTRON DEVICE LETTERS, vol. 29, issue 12, pp 1367-1369, Dec 2008. doi: 10.1109/LED.2008.2006864 Acknowledgment * This research was supported by Brain Korea 21 PLUS Program in 2021, the MOTIE (Ministry of Trade, Industry & Energy 20010836) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device. Figure 1

Design and investigation of triple metal gate engineering of charge plasma based TFET for biomolecule detection

The current manuscript introduces a dielectric regulated charge plasma based Triple metal Gate Tunnel Field Effect Transistor (CPB-TG-TFET) biological sensor. In which a nano-cavity is introduced below the gate and source electrode to detect the biological molecules like amino acids (AAs), protein, etc. The proposed P + and N + regions are contrived depending upon the electrode’s work function on the device’s silicon body. The effects of metal electrode work function modulation, gate electrode length variation and gate oxide thickness variation are analyzed for improving band-to-band tunneling efficiency at the source- channel transition. The proposed structure shows noticeable sensitivity results for neutral and charged biomolecules. The sensitivity of the neutral biomolecules having higher dielectric constant(Kp) is observed higher; the surface potential sensitivity of the Gelatin (Kp = 14) is estimated as 3.×1010 which is 13% and 35% higher than the sensitivity of Keratin (Kp = 10) and Bacteriophage T7 (Kp = 5) respectively at the cavity length of 30 nm.

Dynamic Behavior of Li in Solid-State Li-Ion Batteries Studied using MeV Ion Beam Analysis Techniques

In this review, various studies on the Li depth profiles of metal/electrolyte/metal capacitors and batteries of Au/LCO/LATP/Pt, LCO/LiPON/Si, and LMO/LiPON/NbO with different metal electrodes at both sides (by bias; LCO =LiCoO2, LATP =Li3.1Al0.86Ti1.14Ge1.27P1.73O12, LMO =LiMn2O4, NbO = Nb2O5) using the in-situ reflection ERD (ERD) technique with 9MeV O+4 ion beam and transmission ERD (TERD) technique with 5MeV He+2 ion beam, respectively, are described. For capacitors, the transport fraction of Li-ion in the electrolyte is less than unity. The Li atoms diffuse in the direction opposite to the ion. It has been shown that the batteries are rechargeable. On the other hand, it is observed that an anomalous over-charging takes place when the batteries are over-biased (Si/LiPON/LCO and LMO/LiPON/NbO), and strong reactions of Li with the metal electrodes take place under these conditions. The anomaly observed is explained in terms of the imbalance in the capacities of Li in anode and cathode, which can be attributed to the sizeable amounts of hydrogen present as an impurity during the fabrication of the battery. This is because hydrogen can potentially reduce the capacity of Li in both anode and cathode. The reactions of Li with metal electrodes are discussed in terms of the transport fraction of Li ions (less than unity) and the difference in the work functions of metal electrodes at both sides. Finally, it is noted that the removal of hydrogen in batteries can potentially improve safety, efficiency, and lifetime. These can be achieved by reducing the reaction of Li with metal electrodes. The recoil-scatter method in the TERD technique can measure the Li depth profile in the absence of background yields.

Built‐in bias fields for retention stabilisation in hafnia‐based ferroelectric tunnel junctions

Ferroelectric tunnel junctions have recently attracted a lot of research interest, not only for memory operation but also for e.g. neuromorphic computing. Retention characteristics of these devices are of utmost importance in many applications. The authors have recently demonstrated the feasibility of double-layered ferroelectric tunnel junctions where the ferroelectric hafnium zirconium oxide acts as the memory layer and the dielectric aluminium oxide as the tunnelling barrier. The depolarisation field from the unscreened polarisation charges that is introduced by this structure causes serious limitations on the retention behaviour due to the unintentional back-switching of ferroelectric domains. This leads to a diminishing memory window over time. By using a built-in bias field from different work function metal electrodes, in this case platinum and titanium nitride with 0.85 eV difference, one can shift the polarisation hysteresis curve and counteract the electric depolarisation field. This leads to a more stable on-current over time while only marginally increasing the off-current degradation. Extrapolation to ten years shows a much larger memory window compared to the symmetric metal electrode structure.

Mechanism of charge redistribution at the metal-semiconductor and semiconductor-semiconductor interfaces of metal-bilayer MoS2 junctions.

Layer-number-dependent performance of metal-semiconductor junctions (MSJs) with multilayered two-dimensional (2D) semiconductors has attracted increasing attention for their potential in ultrathin electronics and optoelectronics. However, the mechanism of the interaction and the resulting charge transfer/redistribution at the two kinds of interfaces in MSJ with multilayered 2D semiconductors, namely, the metal-semiconductor (M-S) and the semiconductor-semiconductor (S-S) interfaces, have not been well understood until now, although that is important for the overall Schottky barrier height and the energy-band-offset between different layers of the 2D semiconductors. Here, based on state-of-the-art density functional theory calculations, the mechanisms of bonding and asymmetric electron redistribution at the M-S and S-S interfaces of metal-bilayer MoS2 junctions are revealed. Multiple mechanisms collectively contribute to the electron redistribution at the two kinds of interfaces, and the dominant mechanism depends on both the dimensionality (2D vs 3D) and the work function of metal electrodes. For the M-S interface, the pushback effect and metal-induced gap states play a dominant role for MSJs with 3D metal, while the covalent-like quasi-bonding feature appears for MSJs with medium-work-function 2D metals, and charge transfer plays a main role for MSJs with 2D metals that have very large or small work functions. For the S-S interface, it inherits the electron-redistribution behavior of the M-S interface for MSJs with 2D metal, while opposite electron-redistribution appears in MSJs with 3D metal. These mechanisms provide general insights and new concepts to better understand and use MSJs with multilayered 2D semiconductors.

Interfacing Low‐Temperature Atomic Layer Deposited TiO2 Electron Transport Layers with Metal Electrodes

AbstractLow‐temperature atomic layer deposited (ALD) TiO2 is an electron transport layer that is relatively unreactive with mixed halide perovskite semiconductors. This amorphous, ALD‐grown metal oxide is typically interposed between the perovskite layer and a low work function metal electrode, prompting interest in the electronic and chemical structure of the resulting TiO2/metal interface. Here, the interfaces between TiO2 and two common metal low work function electrodes, polycrystalline thin films of silver and aluminum are studied. It is found that a Schottky barrier forms between Ag and low‐temperature ALD‐grown TiO2, consistent with the observed solar cell current–voltage characteristics, and confirmed by in situ measurement of Ag deposition‐induced core level shifts in X‐ray photoelectron spectra and barrier height extraction from temperature‐dependent current–voltage data. On the other hand, Al reacts chemically with the surface of TiO2 during its deposition. The resulting interface acts as an Ohmic contact, due to the apparent oxygen vacancy doping of the underlying ALD‐TiO2. These findings provide lessons for metal electrode selection in future halide perovskite device structures.

Performance Analysis of Charge Plasma Based Five Layered Black Phosphorus-Silicon Heterostructure Tunnel Field Effect Transistor

In this paper, five layered Black Phosphorus (BP) – Silicon (Si) based Tunnel Field Effect Transistor (TFET) is used to overcome the thermionic limits faced by Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and analysis of the device validates that TFET is a better alternative as nano scale transistor. To enhance the ON state current for five layered BP-Si based TFET, multi electrode (source and drain) based structure is used. For the first time, the charge plasma technique is implemented on BP. The proper work function of metal electrodes has been selected to accordingly implement the charge plasma based technique for BP and Si. Charge plasma will result in generation of electron and hole cloud depending on the work functions at source/drain electrode. Different device properties and characteristics curves viz. IDS-VGS and IDS-VDS are compared for monolayered TFET to five layered based TFET. Different analog/RF properties, as well as linear and distortion parameters of the device such as output conductance (gd), transconductance (gm), cut-off frequency (fT), third order intermodulation distortion, second and third order harmonic distortion, second and third order voltage intercept point and current intercept point, are examined for five layered BP-Si based TFET only. For five layered BP-Si based configuration, the proposed device offers a threshold voltage of 0.42 V, an average subthreshold slope of 24.14 mV/dec, ION of 1.7 × 10−4 A/μm, Drain Induced Barrier Lowering (DIBL) of 1.02 mV/V.