Modern Nanoelectronics Research Articles

Atomic and electronic properties of 2D Chevrel phases: A case study of the superatomic two-dimensional semiconductor Re6Se8Cl2

The design of two-dimensional superatomic materials, which form their atomic structures through covalently bonded clusters with variable chemical compositions, will enable the development of new materials with promised electronic properties that are beneficial for modern nanoelectronics. This paper presents ab initio calculations of the atomic and electronic structures of both bulk and 2D Re6Se8Cl2. The calculations were carried out using density functional theory, incorporating noncollinear spin density and the pseudopotential method. The results include data on the atomic structure, band gap value, formation energy of the Re6Se8Cl2 2D layer, and the redistribution of atomic charges within the structures. The differences in effective masses for electrons and holes in the two-dimensional and bulk Re6Se8Cl2 materials are demonstrated, along with an explanation of how these differences impact their transport properties. The findings are expected to be of great significance for the design, synthesis, and implementation of new two-dimensional superatomic materials with controlled properties in modern nanoelectronics.

Plasmon-mediated dynamics and lasing of nanoemitters enhanced by dispersing nanorings.

We investigate the plasmon-mediated nonlinear dynamics and the optics of a laser emission of random nanoemitters (NEs) embedded in a two-dimensional (2D) lattice of conducting nanorings (NRs) enhanced by plasmon-polariton (PP) excitations. The interaction of quantum NEs with the PP field in the NRs perturbs the dynamics of the electronic populations in NEs, leading to a significant dependence of laser generation (dynamics) on the plasma frequency ωp of PP. This results in a strong coupling of NE field emission with the PP field and sharp variations of the average current in the NR lattice. The phase transition in the system was found when the macroscopic structures of PP fields are excited simultaneously in different regions of the system if ωp (control parameter) reaches critical value ωc. We have established the analytical dependence of the PP current I = I(ωp/ωc) on the plasma frequency, which is in excellent agreement with the results of numerical simulations. This effect may allow the design of new types of PP active devices with the use of conducting NRs in modern nanoelectronics.

Quantum-mechanical study of the optimal phosphorus atoms arrangement on silicene

Manufacturing precise quantum computers with small errors in quantum operations, long coherence times, and low power consumption is the most important challenge in modern nanoelectronics. To understand the operating modes of such calculators in detail, both the optimal arrangement of the qubit system within the structure and changes in its magnetic properties must be comprehensively investigated. In this paper, the behaviour of one and two phosphorus atoms on the surface of silicene is studied using quantum mechanical non-collinear calculations, which consider spin–orbit coupling. The magnetization and ion charge on phosphorus atoms for substitution and different adsorption positions are determined. The optimal positions, binding energies, and activation barriers for the diffusion of adsorbed phosphorus in the presence and absence of a primary adsorbed or substituting phosphorus atom are also established. Overall, the results of this work have important implications for researchers and technologists in the manufacture of Si:P based quantum computers.

Effect of strain and electric field on electronic structure and optical properties of Ga<sub>2</sub>SeTe/In<sub>2</sub>Se<sub>3</sub> heterojunction

Stacking two-dimensional materials into heterogeneous structures is an effective strategy to regulate their physical properties and enrich their applications in modern nanoelectronics. The electronic structure and optical properties of a new two-dimensional Janus Ga<sub>2</sub>SeTe/In<sub>2</sub>Se<sub>3</sub> heterojunction with four stacked configurations are investigated by first principles calculations. The heterojunction of the four configurations is an indirect band-gap semiconductor with a type-II band structure, and the photoelectron donor and acceptor materials are determined by the polarization direction of two-dimensional In<sub>2</sub>Se<sub>3</sub>. The light absorption rises to 25% in the visible region, which is conducive to the effective utilization of the solar visible light. The biaxial strain can induce direct-indirect bandgap transition, and the applied electric field can effectively regulate the bandgap of heterogeneous structure. The bandgap of AA2 configuration increases monotonically from 0.195 eV to 0.714 eV, but that of AB2 configuration decreases monotonically from 0.859 eV to 0.058 eV. The band of the heterojunction always maintains the type-II structure under the two kinds of configurations. The heterojunctions under compressive strain show better light absorption capability in the visible region with shorter wavelength. These results reveal the regulatory mechanism of the Janus Ga<sub>2</sub>SeTe/In<sub>2</sub>Se<sub>3</sub> van der Waals heterojunction electronic structure and provide theoretical guidance in designing novel optoelectronic devices.

Gauge-invariant semidiscrete Wigner theory

A gauge-invariant Wigner quantum mechanical theory is obtained by applying the Weyl-Stratonovich transform to the von Neumann equation for the density matrix. The transform reduces to the Weyl transform in the electrostatic limit, when the vector potential and thus the magnetic field are zero. Both cases involve a center-of-mass transform followed by a Fourier integral on the relative coordinate introducing the momentum variable. The latter is continuous if the limits of the integral are infinite or, equivalently, the coherence length is infinite. However, the quantum theory involves Fourier transforms of the electromagnetic field components, which imposes conditions on their behavior at infinity. Conversely, quantum systems are bounded and often very small, as is, for instance, the case in modern nanoelectronics. This implies a finite coherence length, which avoids the need to regularize non-converging Fourier integrals. Accordingly, the momentum space becomes discrete, giving rise to momentum quantization and to a semi-discrete gauge-invariant Wigner equation. To gain insights into the peculiarities of this theory one needs to analyze the equation for specific electromagnetic conditions. We derive the evolution equation for the linear electromagnetic case and show that it significantly simplifies for a limit dictated by the long coherence length behavior, which involves momentum derivatives. In the discrete momentum picture these derivatives are presented by finite difference quantities which, together with further approximations, allow to develop a computationally feasible model that offers physical insights into the involved quantum processes. In particular, a Fredholm integral equation of the second kind is obtained, where the "power" of the kernel components, measuring their rate of modification of the quantum evolution, can be evaluated.

Electric field control of labyrinth domain structures in core-shell ferroelectric nanoparticles

In the framework of the Landau-Ginzburg-Devonshire (LGD) approach, we studied the possibility of controlling the polarity and morphology of equilibrium domain structures by a homogeneous external electric field in a nanosized ferroelectric core covered with an ultrathin shell of screening charge. Under certain screening lengths and core sizes, the minimum of the LGD energy, which consists of Landau-Devonshire energy, Ginzburg polarization gradient energy, and electrostatic terms, leads to the spontaneous appearance of stable labyrinth domain structures in the core. The labyrinths evolve from an initial polarization distribution consisting of arbitrarily small randomly oriented nanodomains. The equilibrium labyrinth structure is weakly influenced by details of the initial polarization distribution, such that one can obtain a quasicontinuum of nearly degenerate labyrinth structures, whose number is limited only by the mesh discretization density. Applying a homogeneous electric field to a nanoparticle with labyrinth domains, and subsequently removing it, allows inducing changes to the labyrinth structure, as the maze polarity is controlled by a field projection on the particle polar axis. Under specific conditions of the screening charge relaxation, the quasistatic dielectric susceptibility of the labyrinth structure can be negative, potentially leading to a negative capacitance effect. Considering the general validity of the LGD approach, we expect that an electric field control of labyrinth domains is possible in many spatially confined nanosized ferroics, which can be potentially interesting for advanced cryptography and modern nanoelectronics.

Electric Energy Storage Effect in Hydrated ZrO2-Nanostructured System.

The dimensional effect of electric charge storage with a density of up to 270 μF/g by the hydrated ZrO2-nanoparticles system was determined. It was found that the place of localization of different charge carriers is the generalized heterophase boundary-nanoparticles surface. The supposed mechanism of the effect was investigated using the theory of dispersed systems, the band theory, and the theory of contact phenomena in semiconductors, which consists of the formation of localized electronic states in the nanoparticle material due to donor–acceptor interaction with the adsorption ionic atmosphere. The effect is relevant for modern nanoelectronics, microsystem technology, and printed electronics because it allows overcoming the basic physical restrictions on the size, temperature, and operation frequency of the device, caused by leakage currents.

Interfacial Control via Reversible Ionic Motion in Battery‐Like Magnetic Tunnel Junctions (Adv. Electron. Mater. 9/2021)

Controllable Lithium Ion Motion An electronic device inspired by solid-state batteries, comprised of a transition-metal oxide layer and a lithium-containing dielectric as the cathode and electrolyte is presented by Qiang Li, Shandong Li, Guo-Xing Miao, and colleagues in article number 2100512. Controllable lithium ion motion modifies the interfaces and induces resistive switching, while the magnetic configuration generates tunnel magnetoresistance. The combination of ion motion and spin transport integrates iontronics with spintronics and facilitates new capabilities in modern nano-electronics' control toolbox.

Influence of size effects and granule distribution by size on optical and magneto-optical properties of nanocomposites

In this paper, the spectral dependences of the transverse Kerr effect (ТКЕ) are studied experimentally and theoretically. The results are obtained for deposited and annealed samples with a corresponding variation in the size of the granules. It was found that thermomagnetic annealing leads to an increase in the ТКЕ value in magnetic nanostructures, while the most noticeable changes in the effect value were observed in the range of medium and high concentrations of the magnetic component in the visible region of the spectrum. The expediency of using the effective medium approach for calculating magneto-optical effects in granular systems, taking into account the size distribution of granules within the lognormal distribution of granules, is shown. Based on this approach, the main features of the optical and magneto-optical properties of nanocomposites are explained by the example of (Co45Fe45Zr10)X(Al2O3)1–X. All calculations are performed in the Bruggemann approximation, which effectively describes the properties of nanostructures in the region of average concentrations. Size effects are clearly manifested in nanocomposites and have a significant impact on the optical and magneto-optical properties of nanocomposites, especially in the IR region of the spectrum, which is associated with intraband transitions. Taking into account the particle size distribution makes it possible to significantly improve the description of such promising inhomogeneous nanostructures. The solved problem is very important and relevant both from the fundamental point of view – the study of magneto-optical, optical and transport phenomena in nanocomposites – and from the point of view of the great possibilities of their application in modern electronics and nanoelectronics. Taking into account the size effects and the particle size dispersion makes it possible to find new promising functional materials and control their properties in a wide spectral range.

PdPSe: Component‐Fusion‐Based Topology Designer of Two‐Dimensional Semiconductor

AbstractNovel 2D semiconductors play an increasingly important role in modern nanoelectronics and optoelectronics. Herein, a novel topology designer based on component fusion is introduced, featured by the submolecular component integration and properties inheritance. As expected, a new air‐stable 2D semiconductor PdPSe with a tailored puckered structure is successfully designed and synthesized via this method. Notably, the monolayer of PdPSe is constructed by two sublayers via PP bonds, different from 2D typical transition metal materials with sandwich‐structured monolayers. With the expected orthorhombic symmetry and intralayer puckering, PdPSe displays a strong Raman anisotropy. The field‐effect transistors and photodetectors based on few‐layer PdPSe demonstrate good electronic properties with high carrier mobility of ≈35 cm2 V−1 s−1 and a high on/off ratio of 106, as well as excellent optoelectronic performance, including high photoresponsivity, photogain, and detectivity with values up to 1.06 × 105 A W−1, 2.47 × 107%, and 4.84 × 1010 Jones, respectively. These results make PdPSe a promising air‐stable 2D semiconductor for various electronic and optoelectronic applications. This work suggests that the component‐fusion‐based topology designer is a novel approach to tailor 2D materials with expected structures and interesting properties.

A new type of nanoscale reference grating manufactured by combined laser-focused atomic deposition and x-ray interference lithography and its use for calibrating a scanning electron microscope

Calibration of magnification and nonlinearity of scanning electron microscopy (SEM) is an essential task. In this paper, we proposed a new type of 1D grating sample fabricated by combining laser-focused atomic deposition and x-ray interference lithography as a lateral standard for calibrating SEMs. The calibrations of the grating pattern by a metrological large-range atomic force microscope indicate that the grating sample exhibits outstanding pattern uniformity that surpasses conventional samples fabricated by e-beam lithography: (1) the nonlinear deviation of the grating structures is below +/- 0.5 nm over a measurement range of 5 µm; (2) the maximal variation of the calibrated mean pitch values is lower than 0.01 nm at different locations randomly selected all over the pattern area. The proposed new sample is applied for accurately calibrating the magnification and nonlinearity of a commercial SEM, showing its advantages of easy-of-use and high accuracy. The influence of the defocus level of SEM on the calibration result is also demonstrated. This research offers a feasible solution for highly accurate SEM calibration needed for 3D nanometrology and hybrid metrology demanded in metrology of modern nanoelectronics devices and systems.

Atomically sharp interface enabled ultrahigh-speed non-volatile memory devices.

The development of high-performance memory devices has played a key role in the innovation of modern electronics. Non-volatile memory devices have manifested high capacity and mechanical reliability as a mainstream technology; however, their performance has been hampered by low extinction ratio and slow operational speed. Despite substantial efforts to improve these characteristics, typical write times of hundreds of micro- or milliseconds remain a few orders of magnitude longer than that of their volatile counterparts. Here we demonstrate non-volatile, floating-gate memory devices based on van der Waals heterostructures with atomically sharp interfaces between different functional elements, achieving ultrahigh-speed programming/erasing operations in the range of nanoseconds with extinction ratio up to 1010. This enhanced performance enables new device capabilities such as multi-bit storage, thus opening up applications in the realm of modern nanoelectronics and offering future fabrication guidelines for device scale up.

New nanoscale band-to-band tunneling junctionless GNRFETs: potential high-performance devices for the ultrascaled regime

High-performance sub-10-nm field-effect transistors (FETs) are considered to be a prerequisite for the development of nanoelectronics and modern integrated circuits. Herein, new band-to-band tunneling (BTBT) junctionless (JL) graphene nanoribbon field-effect transistors (GNRFETs) endowed with sub-10-nm gate length are proposed using a quantum transport simulation. The nonequilibrium Green’s function (NEGF) formalism is used in quantum simulations considering the self-consistent electrostatics and the ballistic transport limit. The computational assessment includes the IDS–VGS transfer characteristics, the potential and electron density distributions, the current spectrum, the ambipolar behavior, the leakage current, the subthreshold swing, the current ratio, and the scaling capability. It is found that BTBT JL-GNRFETs can provide subthermionic subthreshold swings and moderate current ratios for sub-10-nm gate lengths. Moreover, a new doping profile, based on the use of lateral lightly n-type-doped pockets, is adopted to boost their performance. The numerical results reveal that BTBT JL-GNRFETs with the proposed doping profile can exhibit improved performance in comparison with uniformly doped BTBT JL-GNRFETs. In addition, the role of the length and n-type doping concentration of the pockets in boosting the device performance is also studied and analyzed while considering the scaling capability of such devices, revealing that low doping concentrations and long pocket lengths are useful for performance improvement. The merits of the BTBT JL-GNRFETs based on the proposed nonuniform doping profile, namely sub-10-nm scale, steep subthermionic subthreshold swing, low leakage current, and improved current ratio and ambipolar behavior, make them promising nanodevices for use in modern nanoelectronics and high-performance integrated circuits.

Going beyond the equilibrium crystal shape: re-tracing the morphological evolution in group 5 tetradymite nanocrystals.

Nanocrystals of group 5 tetradymites M2X3 (where M = Bi and Sb, X = Se and Te) are of high technological relevance in modern topological nanoelectronics. However, there is a current lack of a systematic understanding to predict the preferred nanocrystal morphology in experiments where commonly-used equilibrium thermodynamic models appear to fail. In this work, using first-principles DFT calculations with a rationally-extended ab initio atomistic thermodynamics approach coupled to implicit solvation models and Gibbs-Wulff shape constructions, we demonstrate that this absence of predictive power stems from the limitation of equilibrium thermodynamics. By re-tracing and carefully addressing with a more realistic chemical potential definition, we illustrate this shortcoming can be overcome and afford a more rational route to size-engineer and shape-design highly-functional group 5 tetradymite nanoparticles for targeted applications.

A novel band-to-band tunneling junctionless carbon nanotube field-effect transistor with lightly doped pocket: Proposal, assessment, and quantum transport analysis

Overcoming the performance limits encountered with the conventional nanoscale transistors while simplifying the fabrication process is an objective that can give a new impulses to the modern nanoelectronics. A novel band-to-band tunneling junctionless carbon nanotube field-effect transistor, endowed with a lightly doped pocket underneath the coaxial gate, is computationally proposed herein. The quantum simulation based on the non-equilibrium Green's function formalism is used in the investigation while considering the self-consistent electrostatics and ballistic transport conditions. The proposed nanodevice switches via the modulation of band-to-band tunneling in the absence of thermionic emission mechanism. The pocket-induced barrier is employed to mitigate the ambiploar behavior attributed to the thermionic current and to improve the nanodevice performance. The simulations show that the proposed device exhibits improved leakage current, ambipolar behavior, subthermionic subthreshold swing, and current ratio in comparison to those provided by its conventional counterpart uniformly doped. In addition, the role of the pocket length in boosting the performance of the proposed band-to-band tunneling device is investigated, where the optimal length of lightly doped pocket is revealed. Note that the obtained enhancements have been thoroughly analyzed using the energy-position-resolved charge density and current spectrum. The recorded improvements, namely subthermionic subthreshold swing and high ION/IOFF current ratio, together with the merits of junctionless paradigm, make the proposed pocket-based technique, as an intriguing strategy that can be used to boost the performance of similar nanoscale band-to-band tunneling junctionless field-effect transistors for high-performance and low-power applications.

Domain wall conductivity as the origin of enhanced domain wall dynamics in polycrystalline BiFeO3

Despite their primary importance in modern nanoelectronics, conductive domain walls (DWs) can also have a marking effect on the macroscopic response of polycrystalline ferroelectrics. In particular, a large nonlinear piezoelectric response at sub-Hz driving-field frequencies has been previously observed in BiFeO3, which was linked to the conductive nature of the DWs but whose exact origin has never been explained. In this study, by carefully designing the local conductivity in BiFeO3 using chemical doping, we found that the low-frequency piezoelectric nonlinearity is only observed in the sample with a large fraction of conductive DWs. Supported by nonlinear Maxwell–Wagner modeling, we propose that this large response originates from DW displacements inside a specific set of grains or grain clusters in which the internal electric fields are enhanced due to M-W effects. We thus show that these effects likely arise due to the pronounced local anisotropy in the electrical conductivity, varying from grain to grain, whose origin lies in the conductive DWs themselves. The results demonstrate the possibility of controlling the global nonlinear properties of polycrystalline ferroelectrics by engineering local properties.

Sub-10 nm junctionless carbon nanotube field-effect transistors with improved performance

Carbon nanotube field-effect transistors (CNTFETs) and their growing applications are becoming part of modern nanoelectronics, which is in urgent need for high-performance ultrascaled transistors. Sub-10-nm junctionless ballistic carbon nanotube field-effect transistors (JL-CNTFET) with substantial improved performance are computationally proposed herein. The non-equilibrium Green's function (NEGF) simulation is used for the computational assessment. The proposed simple improvement technique is based on the use of high n-type doping concentration at the level of carbon nanotube underneath the gate while keeping the junctionless paradigm that facilitates tremendously the fabrication processes of ultrascaled FETs. It has been found that the proposed doping profile can significantly mitigate several ultrascaling effects while boosting the performance of sub-10-nm JL-CNTFETs. The recorded enhancements include the leakage current, current ratio, subthreshold swing, switching speed, switching energy, drain-induced barrier lowering, and threshold voltage roll-off. The significant improvements obtained in this work for sub-10-nm JL-CNTFETs, make the proposed strategy, which is simple, feasible, and efficient, as a promising technique for improving ultrascaled FETs endowed with other gate geometries and channel nanomaterials while paving the way towards high-performance sub-5-nm FETs.

Tuning the Properties of Zero-Field Room Temperature Ferromagnetic Skyrmions by Interlayer Exchange Coupling.

Magnetic materials offer an opportunity to overcome the scalability and energy consumption limits affecting the semiconductor industry. New computational device architectures, such as low-power solid state magnetic logic and memory-in-logic devices, have been proposed which rely on the unique properties of magnetic materials. Magnetic skyrmions, topologically protected quasi-particles, are at the core of many of the newly proposed spintronic devices. Many different materials systems have been shown hosting ferromagnetic skyrmions at room temperature. However, a magnetic field is a key ingredient to stabilize skyrmions, and this is not desirable for applications, due to the poor scalability of active components generating magnetic fields. Here we report the observation of ferromagnetic skyrmions at room temperature and zero magnetic field, stabilized through interlayer exchange coupling (IEC) between a reference magnet and a free magnet. Most importantly, by tuning the strength of the IEC, we are able to tune the skyrmion size and areal density. Our findings are relevant to the development of skyrmion-based spintronic devices suitable for general-use applications which go beyond modern nanoelectronics.

Accounting for the influence of granule size distribution in nanocomposites

This paper discusses the effect of the distribution of the granules size in nanocomposites on physical properties within the framework of the quasi-classical size effect. Methods of effective medium for describing nanocomposites are discussed. This paper also notes and discusses the contribution of various mechanisms that affect the optical and magneto-optical properties of such structures, especially in the IR region of the spectrum, where the quasi-classical dimensional effect is most pronounced. The Droude-Lorentz mode describes the contribution of the dimensional effect to the diagonal and non-diagonal components of the effective medium's permittivity tensor. The lognormal distribution of the granule size characteristic of many nanostructures is considered. Based on this approach, the dependences of the standard deviation on the value of the integral as a function of the average size of the granules were obtained. Based on the normalization condition, the numerical value of the standard deviation of the r values and the average particle size were analytically determined. This paper also discusses the fundamental significance of the results obtained – the possibility of applying this approach to all possible distributions. The found value of the average size of nanocomposite granules makes it possible to model various properties of nanocomposite structures, first of all, optical and magneto-optical properties, with the help of known methods within the framework of the effective medium approximation. This is especially important for describing the percolation transition in nanocomposites. The problem being solved is important and relevant, since many interesting and important effects are realized in such magnetic nanocomposites, such as the magneto-optical Kerr effect, the anomalous Hall effect, the giant magnetoresistance, and many others. The results obtained allow us to better describe materials that are widely used in modern electronics and nanoelectronics.

Calculation of band structure of the strained germanium nanofilm, doped with a donor impurity

Abstract The band structure of the doped germanium nanofilm grown on the G e ( x ) S i ( 1 − x ) (001) substrate was calculated on the basis of the theory of deformation potential. It was shown that internal mechanical strains exceeding 2% arise in the germanium nanofilm with increasing S i content in the substrate. The presence of such strains leads to the ( L 1 − Δ 1 ) type inversion of the absolute conduction band minimum of the nanofilm. As a result of such radical reconstruction of germanium band structure under deformation, the ionization energy of the donor dopant in the nanofilm is increasing which is explained by the increase of the effective mass of electron and, accordingly, the decrease of the characteristic size of the wave function of electron that is localized on the donor impurity. The dependence of the ionization energy of impurity on the magnitude of the internal strains is due to different values of the baric coefficients of the shift of the energy level of impurity and of the lowest conduction band minimum of the nanofilm. Obtained results can be used in design and modeling of electronic devices and sensors for modern nanoelectronics with pre-set operating characteristics on the basis of strained germanium nanofilm doped with various donors.