Spin Field Effect Transistor Research Articles

Alumina tunnel contact based lateral spin-Field effect transistor

In the present work, modified Datta and Das Type silicon based lateral spin-Field Effect Transistor (MDD Type s-FET) is presented with alumina as tunnel contact. The insertion of alumina enhances the spin injection ability of Co-Graphene nanosheets based ferromagnetic electrode (FM) and also resolves the conductivity mismatch problem. The main accomplishment of present work is that fabricated MDD Type s-FET with alumina as tunnel contact exhibits the non-rectifying current–voltage characteristic with sufficiently large value of MR which is an indispensable requirement of spintronics devices. Also, in present work 2-dimensional electron gas was used as a channel which can control MR through gate voltage. Similarly, the control on MR through gate voltage enables the switching action in s-FET.

Tailoring the spatial-dependent Rashba parameter and spin fluctuations in nanomaterials for improved spin-FET functionality

The spatial fluctuation of the Rashba parameter has been a major issue in the development of state-of-the-art spintronic nanodevices. Since stable spin-precession is of vital importance in the spin field-effect transistor (spin-FET), we have developed a Monte Carlo model to justify that the local E-field of heavy dopants is the origin of the fluctuating Rashba parameter. To maintain a stable drain current in spin-FETs, we study how the size of lattice, doping condition, E-field screening, exchange interaction and temperature influence the Rashba interaction in nanomaterials. Our Monte Carlo model can predict the Rashba effect of Graphene/Nickel(111) substrate at room temperature and presents a path to enhance the Rashba interactions via proximity coupling. More importantly, we have discovered a dip-like structure in the Rashba parameter that strongly scatters the spin states, and we have figured out how to suppress spin fluctuations in the semiconductor channel. Our results are important for the development of the next generation of spin transistors.

Electrically tunable magnetism and unique intralayer charge transfer in Janus monolayer MnSSe for spintronics applications

Controlling magnetism and electronic properties of two-dimensional (2D) materials by purely electrical means is crucial and highly sought for high-efficiency spintronics devices since electric field can be easily applied locally compared with magnetic field. The recently discover 2D Janus crystals has provide a new platform for nanoscale electronics and spintronics due to their broken inversion symmetry nature. The intrinsic ferromagnetic Jauns monolayer, and hence the tunable physical properties, is therefore of great interest. Here, through comprehensive density functional theory calculations and Monte Carlo simulations, we unveil that single-layer MnSSe is an intrinsic ferromagnetic half-metal with a direct band gap of 1.14 eV in spin-down channel and a Curie temperature of about 72 K. The exchange coupling can be significantly enhanced or quenched by hole and electron doping, respectively. In particular, a small amount of hole doping MnSSe can tune its magnetization easy axis in between out-of-plane and in-plane directions, which is conducive to designing 2D spin field-effect transistor for spin-dependent transport. We also find a reversible longitudinal interlayer charge transfer between S and Se layers for the first time that is highly sensitive to the applied external electric field. Interestingly, the directions of charge flow and the applied field are the same. The behavior originates from the coexistence and/or the competition of external and built-in fields. These findings, together with the excellent stability and large in-plane stiffness, can greatly facilitate the development of nanoscale electronics and spintronics devices based on 2D MnSSe crystal.

Electronic states driven by the crystal field in two-dimensional materials: The case of antimonene

The search for novel two-dimensional (2D) giant Rashba semiconductors is a crucial step in the development of spintronic technology. The electronic properties and growth mode of antimonene grown by molecular beam epitaxy were investigated using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy. Results reveal the semiconducting nature of antimonene and the presence of a highly mobile 2D hole gas (2DHG) near the Fermi level. The anisotropy factor and Fermi velocity of the 2DHG are sensitively dependent on the crystal structure and in-plane lattice parameters of antimonene. Antimonene with small lattice parameters exhibits a small anisotropy factor and electron effective mass. Furthermore, the perpendicular (out of plane) electric field breaks the inversion symmetry and, when combined with strong spin-orbit coupling, induces the spin splitting of the valence band of antimonene. ARPES and work function measurements shed light on the band alignment between antimonene and the substrates and confirmed the presence of a nonignorable interface dipole of approximately 0.2 eV. This dipole could be the cause of approximately 80 meV spin splitting at the valence-band maximum of antimonene, a value that is significantly greater than the thermal energy at room temperature. In addition, the spin-splitting degree depends on the interface dipole strength. The gate voltage can generate the out of plane electric field and regulate the spin state similar to an internal electric field. Our results suggest that antimonene and its van der Waals heterostructure system grown on substrates could be used to develop highly efficient spin field-effect transistors and nanospintronic devices.

Spin transport in epitaxial Fe3O4/GaAs lateral structured devices

Research in the spintronics community has been intensively stimulated by the proposal of the spin field-effect transistor (SFET), which has the potential for combining the data storage and process in a single device. Here we report the spin dependent transport on a Fe3O4/GaAs based lateral structured device. Parallel and antiparallel states of two Fe3O4 electrodes are achieved. A clear MR loop shows the perfect butterfly shape at room temperature, of which the intensity decreases with the reducing current, showing the strong bias dependence. Understanding the spin-dependent transport properties in this architecture has strong implication in further development of the spintronic devices for room-temperature SFETs.

Electric field and strain engineering tuning Rashba spin splitting in quasi-one-dimensional organic-inorganic hybrid perovskites (MV)AI3Cl2 (MV = methylviologen, A = Bi, Sb).

We systematically study the Rashba spin texture of lead-free quasi-one-dimensional organic-inorganic hybrid perovskites (OIHP), (MV)AI3Cl2 (MV = methylviologen, A = Bi, Sb) with first-principles calculations. The kx-ky plane Rashba spin splitting was found to depend on the composition of Bi (Sb) and I atoms at band edges. Importantly, increasing ferroelectric polarization and the stretch along the z-direction can effectively enhance the amplitude of the Rashba spin splitting. This work provides an avenue for electric field and strain-controlled spin splitting and highlights the potential of quasi-one-dimensional OIHP for further applications in spin field effect transistors and photovoltaic cells.

Silicene Nanoribbon Based Spin-Field Effect Transistor With Spin Filtering and Spin Seebeck Effects

The present work reports the application of density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism based framework to investigate the voltage-dependent spin transport properties for a Z-shaped silicene nanoribbon (SiNR) based spin-field effect transistor (spin-FET). The structural and magnetic properties of transition metal passivated zigzag-SiNR with symmetric and asymmetric hydrogenation at other ends have been analyzed to identify the suitability of these materials as a potential source and drain electrodes for the proposed spin-FET model. The analysis reveals that the device displays an excellent spin filtering effect and oscillatory transfer characteristics in the parallel configuration (PC) mode. Also, a high drive current and I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{ON}$</tex-math></inline-formula> /I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{OFF}$</tex-math></inline-formula> ratio and both positive and negative transconductance are achieved. Additionally, the device generates a highly spin-polarized thermal current with the spin Seebeck effect and high spin filtration efficiency under the influence of temperature gradient. These findings defend that the proposed device model can be treated as multifunctional spintronic and spin caloritronic devices.

Spin-Orbit Coupling in 2D Semiconductors: A Theoretical Perspective.

This theoretical Perspective reviews spin-orbit coupling (SOC), including the Rashba effect and Dresselhaus effect, in two-dimensional (2D) semiconductors. We first introduce the origin of the Rashba effect and Dresselhaus effect using the Hamiltonian models; we then summarize 2D Rashba semiconductors predicted by first-principles density functional theory (DFT) calculations, including AB binary monolayers, Janus monolayers, 2D perovskites, and so on. We also review various manipulating techniques of the Rashba effect on 2D semiconductors, such as external electric field, strain engineering, charge doping, interlayer interactions, proximity effect of substrates, and external magnetic field. We then briefly summarize the applications of SOC, including the generation, detection, and manipulation of spin currents in spin Hall effect transistors and spin field effect transistors. Finally, we conclude this Perspective and propose three promising research fields of SOC in low-dimensional semiconductors, including the nonlinear SOC Hamiltonian model, 2D ferroelectric SOC semiconductors, and 1D Rashba model and semiconductors. This theoretical Perspective enriches the fundamental understanding of SOC in 2D semiconductors and will help in the design of new types of spintronic devices in future experiments.

Gate-Voltage-Modulated Spin Precession in Graphene/WS2 Field-Effect Transistors

Transition metal dichalcogenide materials are studied to investigate unexplored research avenues, such as spin transport behavior in 2-dimensional materials due to their strong spin-orbital interaction (SOI) and the proximity effect in van der Waals (vdW) heterostructures. Interfacial interactions between bilayer graphene (BLG) and multilayer tungsten disulfide (ML-WS2) give rise to fascinating properties for the realization of advanced spintronic devices. In this study, a BLG/ML-WS2 vdW heterostructure spin field-effect transistor (FET) was fabricated to demonstrate the gate modulation of Rashba-type SOI and spin precession angle. The gate modulation of Rashba-type SOI and spin precession has been confirmed using the Hanle measurement. The change in spin precession angle agrees well with the local and non-local signals of the BLG/ML-WS2 spin FET. The operation of a spin FET in the absence of a magnetic field at room temperature is successfully demonstrated.

Spin-Current Modulation in Hexagonal Buckled ZnTe and CdTe Monolayers for Self-Powered Flexible-Piezo-Spintronic Devices.

The next-generation spintronic device demands the gated control of spin transport across the semiconducting channel through the replacement of the external gate voltage source by the piezo potential, as experimentally demonstrated in Zhu et al. ACS Nano, 2018, 12 (2), 1811-1820. Consequently, a high level of out-of-plane piezoelectricity together with a large Rashba spin splitting is sought after in semiconducting channel materials. Inspired by this experiment, a new hexagonal buckled two-dimensional (2D) semiconductor, ZnTe, and its iso-electronic partner, CdTe, are proposed herewith. These 2D materials show a strong spin-orbit coupling (SOC), which is evidenced by a large Rashba constant of 1.06 and 1.27 eV·Å, respectively, in ZnTe and CdTe monolayers. Moreover, these Rashba semiconductors exhibit a giant out-of-plane piezoelectric coefficient (d33) = 88.68 and 172.61 pm/V, and can thereby generate a high piezo potential for gating purposes in spin field-effect transistors (spin-FETs). While the low elastic stiffness implies the mechanical flexibility or stretchability in these monolayers. The Rashba constants are found to be effectively modulated via external perturbations, such as strain and electric field. The wide band gap provides ample room for modulation in its electronic properties via external perturbations. Such scope is severely limited in previously reported narrow band gap Rashba semiconductors. The fascinating results found in this work indicate their great potential for applications in next-generation self-powered flexible-piezo-spintronic devices. Moreover, a new class of hexagonal buckled ZnX (X: S, Se, or Te) monolayers is proposed herein based on their previously synthesized bulk counterparts, while their electronic, mechanical, piezoelectric, and thermal properties have been thoroughly investigated using the state-of-art density functional theory (DFT).

Strain-controlled Rashba spin-orbit coupling effect in SnS and SnSe monolayers

The miniaturization of transistors and the high density of integrated circuits makes conventional transistors reach a size limit, causing leakage currents, unstable performance, and increasing production cost. Spin field effect transistors (SFETs) based on spintronics use electron spin as an information carrier and regulate electron spin degree of freedom for storing and processing information. As a class of spintronics, Rashba spin–orbit coupling (SOC) effect attracts increasing attention because of its electric tunability. SFETs based on Rashba SOC and two-dimensional materials will make a qualitative leap in future semiconductor devices. Based on first-principles calculations, it is found that the applied strains along zigzag (ZZ), armchair (AC), and biaxial direction make the bandgaps of SnS and SnSe monolayers (ML) have an indirect-direct-zero transition. SnS and SnSe ML have a more stable electron spin and stronger Rashba spin splitting than InGaAs/InAlAs heterojunction and Au(111) surface. For SnS ML, 6% tensile strain along ZZ direction not only stabilizes the electron spin but also strengthens Rashba spin splitting to a maximum of 0.76 eV Å. For SnSe ML, 2% tensile strain along biaxial direction makes Rashba spin splitting strength reach a maximum of 1.33 eV Å.

Electrical Control of Valley-Zeeman Spin-Orbit-Coupling-Induced Spin Precession at Room Temperature.

The ultimate goal of spintronics is achieving electrically controlled coherent manipulation of the electron spin at room temperature to enable devices such as spin field-effect transistors. With conventional materials, coherent spin precession has been observed in the ballistic regime and at low temperatures only. However, the strong spin anisotropy and the valley character of the electronic states in 2D materials provide unique control knobs to manipulate spin precession. Here, by manipulating the anisotropic spin-orbit coupling in bilayer graphene by the proximity effect to WSe_{2}, we achieve coherent spin precession in the absence of an external magnetic field, even in the diffusive regime. Remarkably, the sign of the precessing spin polarization can be tuned by a back gate voltage and by a drift current. Our realization of a spin field-effect transistor at room temperature is a cornerstone for the implementation of energy efficient spin-based logic.

Diffusive Spin Transport in Narrow Two-Dimensional-Electron-gas Channels

Using the geometry of the spin field-effect transistor, we investigate the spin transport of in-plane spins in an array of narrow channels formed in a two-dimensional electron gas confined in an $(\mathrm{In},\mathrm{Ga})\mathrm{As}$ quantum well. We demonstrate a clear enhancement of the spin-diffusion length with decreasing channel width, yielding up to 10 \textmu{}m for the narrowest channels. We discuss the observed enhancement in terms of the suppression of the Dyakonov-Perel mechanism of spin relaxation, which has been invoked in previous studies in the case of diffusion of out-of-plane oriented spins. We also show that the spin signal is significantly higher when injecting into an array of narrow channels, compared with injecting into a single narrow channel.

CrI3/Y2CH2 Heterointerface-Induced Stable Half-Metallicity of Two-Dimensional CrI3 Monolayer Ferromagnets.

Two-dimensional (2D) CrI3 monolayer ferromagnets are key to the development of future miniature spintronic devices and modulating them into a half-metal will greatly expand the application scenarios of CrI3 in nanospintronics. Nevertheless, existing strategies to induce half-metallicity of a CrI3 monolayer remain experimentally challenging and have unstable issues. In this work, the introduction of a 2D electride [Y2C]2+·2e- as an auxiliary layer is shown to be an effective way to achieve the generation of stable half-metallicity in the CrI3 monolayer. When the fully hydrogenated Y2CH2 and ferromagnetic CrI3 monolayer combine to form a heterostructure, surprisingly the appropriate amount of charge injection (0.72 e) turns CrI3 into a half-metal. Hetero-interfacial half-metallicity in CrI3 is an intrinsic one and does not require any chemical functionalization or external physical modification. Therefore, it is advantageous for practical applications of CrI3 in miniature spintronic devices, such as magnetic tunnel junctions, spin valves or spin field-effect transistors. A new strategy of the stable CrI3/Y2CH2 heterostructure was successfully developed to induce the half-metallicity of 2D CrI3 ferromagnets, which is experimentally feasible and half-metallic stable enough. This work paves the way for the application of the CrI3 monolayer in half-metallic-based spintronics.

Band structure engineering of van der Waals heterostructures using ferroelectric clamped sandwich structures

A novel strategy of band structure engineering of van der Waals heterostructure is proposed using a ferroelectric (FE) clamped sandwich structure from first principles. The validity of the strategy is demonstrated in the sandwich structure of ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$/bilayer-${\mathrm{CrI}}_{3}/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (${\mathrm{In}}_{2}{\mathrm{Se}}_{3}/\mathrm{bi}\ensuremath{-}{\mathrm{CrI}}_{3}/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$) made by ferroelectric ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ layers and semiconducting bilayer (SB) ${\mathrm{CrI}}_{3}$. Four states with different band structures in the FE/SB/FE sandwich structure are obtained by switching the FE polarization in the top and bottom ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ layers. Two of the states possess spin-splitting semiconducting band structures with opposite spin channel in conduction bands which are generated from a spin-degenerated band structure of the ${\mathrm{CrI}}_{3}$ bilayer, resulting in an electric field controllable and nonvolatile four states spin-field effect transistor. The strategy of using FE layers to engineer band structures and generate spin-splitting semiconducting band structure in van der Waals heterostructure opens a new route in two-dimensional electronics and spintronics.

A room-temperature four-terminal spin field effect transistor

In analogy to the central role of transistors in conventional electronics, a key device in spintronics, spin field effect transistor (spin FET), has been predicted theoretically. Several approaches have been explored, but their applications remain a considerable challenge due to the small spin signals and low working temperature. In this work, we report a four-terminal spin FET using an individual SWNT with two partially open segments and the working mechanisms is closely related to the magnetic moments at these segments. The spin-related signals ( R spin ) can be as large as several hundred Ohm and the spin FET works at room temperature under atmospheric conditions. R spin can be modulated with gate voltages and external magnetic fields. The realization of spin FET may lead to the development of integrated circuit of spintronics, which is fundamentally different from charge-based conventional electronics. • Room-temperature ferromagnetic semiconductor: semiconducting SWNT with open segments. • Pure spin current induced by a conventional charge current in a fully separated path. • Spin FET working at room temperature under atmospheric conditions. • Ohmic contact between SWNT and Mo is an efficient spin injector/detector. • R spin can be modulated with gate voltages and external magnetic fields.

Direct band gap and strong Rashba effect in van der Waals heterostructures of InSe and Sb single layers

Van der Waals heterostructures formed by stacking different types of 2D materials are attracting increasing attention due to new emergent physical properties such as interlayer excitons. Recently synthesized atomically thin indium selenide (InSe) and antimony (Sb) individually exhibit interesting electronic properties such as high electron mobility in the former and high hole mobility in the latter. In this work, we present a first-principles investigation on the stability and electronic properties of ultrathin bilayer heterostructures composed of InSe and Sb single layers. The calculated electronic band structures reveal a direct band gap semiconducting nature of the InSe/Sb heterostructures independent of stacking pattern. Taking spin–orbit coupling (SOC) into account, we find a large Rashba spin splitting at the bottom of conduction band, which originates from the atomic SOC with the symmetry breaking in the heterostructure. The strength of the Rashba spin splitting can be tuned by applying in-plane biaxial strain or an out-of-plane external electric field. The presence of large Rashba spin splitting together with a suitable band gap in InSe/Sb bilayer heterostructures make them promising candidates for spin field-effect transistor and optoelectronic device applications.

Polarity Effect on the Electronic Structure of Molybdenum Dichalcogenides MoXY (X, Y = S, Se): A Computational Study Based on Density-Functional Theory

Computational research based on the Density Functional Theory (DFT) has been performed to explore the electronic structure of monolayer material Transition Metal Dichalcogenides (TMDCs) Molybdenum Dichalcogenides MoXY (X; Y = S; Se) in the first Brillouin zone by breaking its mirror symmetry due to the polarity effect. Our study discovered that Rashba spin-splitting could be identified around the Γ point by proposing the polarity effect on the system. Moreover, the anisotropic characteristic of Rashba spin-splitting in this system can be explicitly analyzed by using perturbation theory and the third-order symmetry group analysis. By performing the spin textures analysis, this research also recognizes the in-plane direction of spin textures. The tunable characteristic of the Rashba parameter of this monolayer polar MoSSe system under the strain effects control exhibits its potential to be the candidate of semiconductor material for the Spin Field Effect Transistor (SFET) device.

Tunable Rashba Spin Splitting in Two-Dimensional Polar Perovskites.

Two-dimensional (2D) Rashba semiconductors with structure inversion asymmetry and a spin-orbit coupling (SOC) effect show promising applications in nanospintronics, such as spin field effect transistors (FETs). Here, we systematically investigate the electronic structures and Rashba effect of 2D polar perovskites ABX3 (A = Cs+ or Rb+; B = Pb2+ or Sn2+; X = Cl, Br, or I) by first-principles density functional theory calculations. We demonstrate that, except for the cubic case, 2D polar perovskites from tetragonal and orthorhombic three-dimensional (3D) bulks exhibit a strong intrinsic Rashba effect around the Γ point, due to their structure inversion asymmetry and the strong SOC effect of heavy atoms. In particular, 2D orthorhombic RbSnI3 shows the largest Rashba constant of 1.176 eV Å among these polar perovskites, which is comparable to that of 3D bulk perovskites previously reported in experiments and theory. Furthermore, several 2D polar perovskites also show a strong electric field response. In particular, 2D tetragonal RbPbI3 and tetragonal CsPbI3 have strong electric field responses of >0.5 e Å2. Therefore, 2D polar perovskites as promising Rashba semiconductors possess large Rashba constants and strong electric field responses, resulting in a short spin channel length of tens of nanometers to preserve the spin coherence in spin FETs, superior to conventional 3D micrometer spin FETs.

Interference effect in the electronic transport of a topological insulator quantum dot

Edge and bulk energy levels can coexist in a quantum dot (QD) made of a topological insulator. Interference effect will occur between bulk and edge levels and also between degenerate edge levels. It can be observed in the transport behavior. For the former, it acts as Fano interference with edge and bulk levels contributing continuous and resonant transport channels, respectively. Generally speaking, Fano interference can be realized in a two-armed junction with a single QD or a one-armed junction with at least two QDs. But here it is realized in a one-armed junction with a single QD. As for the interference between degenerate edge levels, it leads to a spin and space dependent scattering process. Spin of an incident electron will either be conserved or rotate about an axis for transmitting into different leads. It is determined by the local spin polarization of edge levels and the accumulated phase in transport paths in the QD. It may be used in the design of a spin field-effect transistor.