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In order to solve the problems of low absorption efficiency and small frequency range of traditional terahertz (THz) detectors, a broadband terahertz metasurface pyroelectric detector was proposed by combining a dual metasurface absorption array structure with the LiTaO3 pyroelectric detector. The optimization method of MATLAB and CST co-simulation was used to optimize the metasurface structure on demand. ANSYS was used to simulate and analyze the pyroelectric detector, and the influence of characteristic parameters such as sensitive layer and adiabatic layer on the temperature change rate and response current of terahertz pyroelectric detector was obtained. The results show that the use of metasurface array structure improves the detection performance of the whole THz band, and the average pyroelectric current output of the stool-type pyroelectric detector under given conditions is 31.52 pA. The use of metasurface as an absorption structure can make the pyroelectric detector have continuous and efficient wave absorption characteristics, which provides some reference for the design of broadband terahertz detectors.

This article discusses the main trends in the physics and preparation of metal oxides and summarizes the results of research published by SPQEO in this area over the past decade. The main metal oxides studied include ZnO, Zn1-xCdxO, Zn1-xCoxO, MgxZn1– xO, ZnO:Mn, VO2, ZrO2–Y2O3, TiO2, WO3, Gd2O3, Er2O3, WO3–CaO–SiO2–B2O3: Tb3+, Dy2O3, NiO, FexOy, Ga2O3, Al2O3, ITO, Ag2O and graphene oxide. These oxides were obtained by the following methods: sintering in air or in a stream of various gases, magnetron sputtering, atomic layer deposition, explosive evaporation, sol-gel, spin coating, spray pyrolysis, rapid thermal annealing, green synthesis from plant solutions, melt quenching, rapid thermal annealing, self-ignition, ion-plasma co-sputtering, vacuum sputtering, reactive ion beam sputtering, and the Hammer method. The electrical and optical properties of the studied oxides are illustrated. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Ukrainian journal Semiconductor Physics, Quantum Electronics and Optoelectronics (SPQEO) was launched in 1998 artificially combining three main areas of scientific activity inherent to the V. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, namely semiconductor physics, quantum electronics and optoelectronics. After a decade this artificial base turned into some kind of organic symbiosis, namely: (i) the main optoelectronic systems are based on semiconductor devices, for example, fiber-optic networks; (ii) semiconductor lasers dominate in a huge number of applications in quantum electronics; (iii) semiconductor physics proposes new types of LEDs with extremely high efficiency, and so on. This article is dedicated to the 25th anniversary of SPQEO. According to the Google Scholar Citation statistics, above 1680 articles cited more than 7350 times in total were published in the journal from 1998 to 2023. The statistics of references of journal articles and the scientific areas of the most cited articles are presented. [ABSTRACT FROM AUTHOR]

A previous study by Mantas and Vecil (Int J High Perform Comput Appl 34(1): 81–102, 2019) describes an efficient and accurate solver for nanoscale DG MOSFETs through a deterministic Boltzmann-Schrödinger-Poisson model with seven electron–phonon scattering mechanisms on a hybrid parallel CPU/GPU platform. The transport computational phase, i.e. the time integration of the Boltzmann equations, was ported to the GPU using CUDA extensions, but the computation of the system's eigenstates, i.e. the solution of the Schrödinger-Poisson block, was parallelized only using OpenMP due to its complexity. This work fills the gap by describing a port to GPU for the solver of the Schrödinger-Poisson block. This new proposal implements on GPU a Scheduled Relaxation Jacobi method to solve the sparse linear systems which arise in the 2D Poisson equation. The 1D Schrödinger equation is solved on GPU by adapting a multi-section iteration and the Newton-Raphson algorithm to approximate the energy levels, and the Inverse Power Iterative Method is used to approximate the wave vectors. We want to stress that this solver for the Schrödinger-Poisson block can be thought as a module independent of the transport phase (Boltzmann) and can be used for solvers using different levels of description for the electrons; therefore, it is of particular interest because it can be adapted to other macroscopic, hence faster, solvers for confined devices exploited at industrial level. [ABSTRACT FROM AUTHOR]

This paper describes utilizing open‐source numerical simulation software, typically used in solar photovoltaics research, as an attractive supplementary educational tool for teaching the underlying physics and operation of P‐N junction diodes. Details of educational P‐N device models and simulation‐based learning scenarios developed for this purpose are provided here. The presented approach allows students to learn the essential concepts related to P‐N diodes experientially. These include some frequently observed nonidealities, closely mimicking experimental I‐V measurements. Unlike most educational tools in this field, all simulations demonstrated here are performed locally on the student's computer using free and portable software, which eliminates the need for a live internet connection or time‐consuming installations, making it easier to implement in a classroom and much more accessible to students. The paper also discusses the implementation of this supplementary tool and reports the results of a survey conducted to measure student satisfaction with it and its implementation approach. The presented method can be adapted to suit the needs of undergraduate and graduate students studying engineering courses that require an introduction to semiconductor devices. The details of P‐N diode device models are introduced and discussed so that users can modify them in accordance with their practical or educational purposes. [ABSTRACT FROM AUTHOR]

An active region design based on InGaN / delta-InN quantum well (QW) with AlGaN interlayer (IL) and GaN barriers (delta-structure) is investigated for potential high-efficiency visible light emitters. Numerical simulations demonstrate a large wavelength redshift with a simultaneous increase of the electron-hole wavefunction overlap for the delta-structure as compared to the conventional InGaN QW with AlGaN IL and GaN barriers. Proof of concept experimental growths via the metalorganic chemical vapor deposition demonstrate the effect of the delta-InN insertion into the conventional InGaN-based QW. [ABSTRACT FROM AUTHOR]

Experimental results from literature show equidistant energy levels in thin Bi films on surfaces, suggesting a harmonic oscillator description. Yet this conclusion is by no means imperative, especially considering that any measurement only yields energy levels in a finite range and with a nonzero uncertainty. Within this study we review isospectral potentials from the literature and investigate the applicability of the harmonic oscillator hypothesis to recent measurements. First, we describe experimental results from literature by a harmonic oscillator model, obtaining a realistic size and depth of the resulting quantum well. Second, we use the shift-operator approach to calculate anharmonic non-polynomial potentials producing (partly) equidistant spectra. We discuss different potential types and interpret the possible modeling applications. Finally, by applying nth order perturbation theory we show that exactly equidistant eigenenergies cannot be achieved by polynomial potentials, except by the harmonic oscillator potential. In summary, we aim to give an overview over which conclusions may be drawn from the experimental determination of energy levels and which may not. [ABSTRACT FROM AUTHOR]

This article investigates ambipolar organic field-effect transistors, which can exhibit a spatially localized photoelectric effect. This effect consists in the fact that a transistor channel has a narrow photosensitive region in which incident radiation is converted into a photocurrent. The spatial position of which can be controlled by changing the gate voltage . Due to this, the dependence of the photocurrent on can reproduce the spatial distribution of the incident radiation intensity. In this work, the response time of phototransistors is studied by numerical modeling. In particular, it is shown that the response time to turning light on in a stepwise manner is a few nanoseconds, while the response time to voltage switching is a few microseconds. The article also studies how changes in various parameters of a phototransistor affect its efficiency. It is shown that the simultaneous improvement of external quantum efficiency (EQE), the photocurrent-to-dark-current-ratio (), the spatial resolution, and the response time can be achieved by reducing the channel length. It is also shown that the use of active layer materials in which photogenerated electron–hole pairs are larger than 1 nm can provide higher EQE values and without any significant reduction in spatial and temporal resolution. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots are currently emerging as one of the most promising sources of non-classical light on which to base future quantum networks. They can generate single photons as well as pairs of entangled photons with unprecedented brightness, indistinguishability, and degree of entanglement. These features have very recently opened up the possibility to perform advanced quantum optics protocols that were previously inaccessible to single quantum emitters. In this work, we report on two experiments that use the non-local properties of entanglement to teleport quantum states: three-photon state teleportation and four-photon entanglement teleportation. We discuss all the experimental results in light of a theoretical model that we develop to account for the non-idealities of the quantum source. The excellent agreement between theory and experiment enables a deep understanding of how each parameter of the source affects the teleportation fidelities and it pinpoints the requirements needed to overcome the classical limits. Finally, our model suggests how to further improve quantum-dot entangled-photon sources for practical quantum networks. [ABSTRACT FROM AUTHOR]

In order to investigate the full potential of the Electrical Impedance Spectroscopy (EIS) when used to address various aspects of conductive and dielectric response within the field of Condensed Matter Physics and Electrochemistry, a new analysis of the electrical impedance experiments has been undertaken. Within the framework of quantum mechanical band structure and using the concept of electrochemical potential for each of the relevant energies, the problem of electrical response in condensed phase has been formulated, using augmented Maxwell equations of Classical Electrodynamics, as a boundary value problem of a set of coupled, non-linear parabolic equations in energy, space and time. The result of this numerical analysis is a principal possibility of a complete electrical characterisation of both monocrystals, glassy solids and liquids. The EIS has been put in this way on a new qualitative level and should be considered now as the most general electrical experimental characterisation tool available. In this article, a methodology of numerical simulations of electrical response in condensed matter systems at classical frequencies (from ~1 THz down to dc) is presented and the numerical simulation results are then discussed, using monocrystalline Silicon, chalcogenide glass ion conductor Agx(AsS2)1−x and simple aqueous chloride solution as experimental test cases. Some other unique results of the new EIS analysis will also be discussed. These include the possibility of a clear distinction between the contribution to the electrical response from bound and mobile electrical charges, the possibility of simultaneous and independent determination of the mobile electrical charges mobility and their density in one EIS experiment and incorporation of the interfacial regions of the system under test (SUT) as an essential part of the overall electrical response. [ABSTRACT FROM AUTHOR]

A physics-based compact model of silicon carbide (SiC) junction barrier Schottky diode for circuit simulation is developed in this paper. The semiconductor physics mechanism in SiC, such as temperature-dependent mobility and incomplete ionization, are considered. The detailed device parameters, including drift region concentration, drift thickness, active area, and Schottky barrier height, are modeled. Then, a datasheet-oriented parameter extraction procedure for the device parameters is presented for three kinds of commercial SiC Schottky diodes with junction barrier structure. The model is implemented in the circuit simulator PSpice. In order to verify this model, the Technology Computer-Aided Design Sentaurus simulation is conducted with the device parameters and physical models, which shows a good agreement with the PSpice simulation. [ABSTRACT FROM AUTHOR]

The current–voltage (J–V) curves of Al/TiO2/n‐Si structures present an anomalous behavior where the current becomes constant for a reverse bias higher than ≈0.65 V. Here we analyze devices fabricated by spin‐coating of an organometallic precursor and subsequent annealing in an O2 atmosphere. The details of the current saturation phenomenon are interpreted as a consequence of the formation of a depletion region in Si, which limits the voltage drop in the film and truncates the current. The analysis is supported experimentally by capacitance–voltage and photoconductance measurements. It is also shown that the saturation current can be controlled by modifying the film's deposition conditions, changing the barrier for electron injection from Al to TiO2. [ABSTRACT FROM AUTHOR]

Simulation of terahertz (THz) emission based on PC antennas imposes a challenge to couple the semiconductor carrier phenomena, optical transport and the THz energy transport. In this paper a Multi-physics simulation for coupling these phenomena using COMSOL Multi-physics 4.3b is introduced. The main parameters of THz photoconductive (PC) antenna as THz emitter have been reviewed and discussed. The results indicate the role of each parameter in the resulting photocurrent waveform and THz frequency: The radiated THz photocurrent waveform is determined by the photoconductive gap (the separation between the metallic electrodes), the incident laser illumination and the DC excitation voltage; while the THz frequency depends on the dipole length. The optimization of these parameters could enhance the emission. The simulations extend the advance of compact and cost-effective THz emitters.

The concept of electric current is fundamental in the study of electrical engineering (EE). Students are often exposed to this concept in their daily lives and early in middle school education. Lower-division university courses are usually limited to the study of passive electronic devices and simple electric circuits. Semiconductor physics is an upper-division course that presents the physics behind semiconductor devices in depth and exposes the students to microscale explanations of different types of current, such as drift and diffusion currents. This paper investigates how third-year college students majoring in EE link microscale and macroscale concepts of current, and what misconceptions they reveal after one quarter of advanced instruction in semiconductor physics. The interviewees were posed a problem, based on a distracting device structure that exposed student difficulties in defining current, charges and doping, and the plotting of current–voltage (I–V) characteristics. For example, some students had the naïve idea that current is the flow of a particular type of charge (i.e., only electrons or only holes) or that there is a “spectrum of doping.” Almost all students drew a one-quadrant coordinate system for the I–V curves, which might imply that students think only about positive voltages. These findings can inform further studies to identify and address misconceptions in the important area of semiconductor device physics. [ABSTRACT FROM PUBLISHER]

This article proposes, as an educational innovation, the introduction of notions of semiconductor physics in the Compulsory Secondary Education, so that students at this stage may acquire a basic knowledge of the physical foundations of electronics. Under the general hypothesis that it is possible to integrate some of these basic notions on the topic into the physics and chemistry class, a series of specific hypotheses that guide the integration are established. These imply the need to knowing the students’ most frequents ideas and learning obstacles regarding the topic, in order to identify the learning demand. Then, a didactic transposition of the semiconductor physics to the said educational stage is proposed, indicating (a) the contents of physics and chemistry curriculum that serve as bridge between the knowledge that the students already have and what they are going to learn, and (b) the didactic treatment of the new contents along with the learning objects.

Probing students' conceptual understanding and misconceptions of key engineering concepts is a rich area of research. Given the importance of modern electronics in today's world, it is essential for many engineers, particularly device designers from electrical engineering, to have a robust conceptual knowledge of how electronic devices work. The P-N junction diode is the building block of more advanced semiconductor devices. This exploratory study investigates the representations that students use to describe the behavior of a P-N junction diode. Participants were 3rd year students enrolled in a required introductory course in semiconductor physics. Each student participated in a one hour individual semi-structured "think-aloud" interview where he/she had to conceptually solve problems related to P-N junction diodes. Although these semiconductor physics courses aim to develop foundational knowledge for future device design engineers; the results of this study suggest that even successful upper division students majoring in electrical engineering may not have a good conceptual grasp of key concepts related to the diode by the end of the course. For example, many could not correctly differentiate between the linear (or resistive) behavior of an N-N junction and the non-linear behavior of a P-N junction diode. Half of the students in this study did not use their previous knowledge including current-voltage (I-V) curves to perform reality checks. The students struggled with both the macro-level behavior of a P-N junction diode and the underlying micro-level phenomena. By investigating the roots of students' challenges, this study supports the need for new teaching approaches to facilitate better conceptual understanding in introductory semiconductor physics courses. [ABSTRACT FROM AUTHOR]

A double layer solid oxide fuel cell (DLSOFC) without using the electrolyte (layer) has been designed by integrating advantages of positive electrode material of lithium ion battery(LiNi 0.8 Co 0.15 Al 0.05 O 2 ) and oxygen-permeable membranes material (trace amount cobalt incorporated terbium doped ceria, TDC + Co) based on the semiconductor physics principle. Instead of using an electrolyte layer, the depletion layer between the anode and cathode served as an electronic insulator to block the electrons but to maintain the electrolyte function for ionic transport. Thus the device with two layers can realize the function of SOFC and at the same time avoids the electronic short circuiting problem. Such novel DLFC showed good performance at low temperatures, for instance, a maximum power density of 230 mWcm −2 was achieved at 500 °C. The working principle of the new device is presented. [ABSTRACT FROM AUTHOR]

Superconductivity of n-doped SrTiO3, which remained enigmatic for half a century, is treated as a particular case of nonadiabatic phonon pairing. Motivated by experiment, we suggest the existence of the mobility edge at some dopant concentration. The itinerant part of the spectrum consists of three conduction bands filling by electrons successively. Each subband contributes to the superconducting instability and exhibits a gap in its energy spectrum at low temperatures. We argue that superconductivity of n-doped SrTiO3 results from the interaction of electrons with several longitudinal (LO) optical phonons with frequencies much larger than the Fermi energy. Immobile charges under the mobility edge threshold increase the "optical" dielectric constant far above that in clean SrTiO3 placing control on the electron-LO phonon interaction. TC initially grows as density of states at the Fermi surface increases with doping, but the accumulating charges reduce the electrons-polarphonon interaction by screening the longitudinal electric fields. The theory predicts maxima in the TC-concentration dependence indeed observed experimentally. Having reached a maximum in the third band, the transition temperature finally decreases, rounding out the TC (n) dome, the three maxima with accompanying superconducting gaps emerging consecutively as electrons fill successive bands. This arises from attributes of the LO optical phonon pairing of electrons. The mechanism of LO phonons opens the path to increasing superconducting transition temperature in bulk transition-metal oxides and other polar crystals, and in charged 2D layers at the LaAaO3/SrTiO3 interfaces and on the SrTiO3 substrates. [ABSTRACT FROM AUTHOR]

Superconductivity of n-doped SrTiO3, which remained enigmatic for half a century, is treated as a particular case of nonadiabatic phonon pairing. Motivated by experiment, we suggest the existence of the mobility edge at some dopant concentration. The itinerant part of the spectrum consists of three conduction bands filling by electrons successively. Each subband contributes to the superconducting instability and exhibits a gap in its energy spectrum at low temperatures. We argue that superconductivity of n-doped SrTiO3 results from the interaction of electrons with several longitudinal (LO) optical phonons with frequencies much larger than the Fermi energy. Immobile charges under the mobility edge threshold increase the "optical" dielectric constant far above that in clean SrTiO3 placing control on the electron-LO phonon interaction. TC initially grows as density of states at the Fermi surface increases with doping, but the accumulating charges reduce the electrons-polarphonon interaction by screening the longitudinal electric fields. The theory predicts maxima in the TC-concentration dependence indeed observed experimentally. Having reached a maximum in the third band, the transition temperature finally decreases, rounding out the TC (n) dome, the three maxima with accompanying superconducting gaps emerging consecutively as electrons fill successive bands. This arises from attributes of the LO optical phonon pairing of electrons. The mechanism of LO phonons opens the path to increasing superconducting transition temperature in bulk transition-metal oxides and other polar crystals, and in charged 2D layers at the LaAaO3/SrTiO3 interfaces and on the SrTiO3 substrates. [ABSTRACT FROM AUTHOR]

The author describes the practical of the research library in the Institute of Semiconductor Physics with information retrieval classification systems and the advantages of the use of multidimentional indexing for research documents from the view point of information retrieval and search on the particular thematic requests.

A heterojunction is the key junction for charge extraction in many thin film solar cell technologies. However, the structure and band alignment of the heterojunction in the operating device are often difficult to predict from calculations and, due to the complexity and narrow thickness of the interface, are difficult to measure directly. In this study, we demonstrate a technique for direct measurement of the band alignment and interfacial electric field variations of a fully functional lead halide perovskite solar cell structure under operating conditions using hard X-ray photoelectron spectroscopy (HAXPES). We describe the design considerations required in both the solar cell devices and the measurement setup and show results for the perovskite, hole transport, and gold layers at the back contact of the solar cell. For the investigated design, the HAXPES measurements suggest that 70% of the photovoltage was generated at this back contact, distributed rather equally between the hole transport material/gold interface and the perovskite/hole transport material interface. In addition, we were also able to reconstruct the band alignment at the back contact at equilibrium in the dark and at open circuit under illumination.

A method for the nondestructive contactless control of thickness of undoped autoepitaxial InAs layers on heavily-doped substrates by Fourier-Transform Infrared Spectroscopy (FTIR) is implemented. The studied layers are grown by the chloride-hydride epitaxy method in a vertical reactor. The thickness control method is based on the analysis of interference patterns observed in infrared reflectance spectra. Recommendations are made on the choice of the measurement spectral range optimal for the InAs structures. The choice is determined by the minimal change of the InAs refraction index, and features of reflectance of the heavily-doped substrates. A good agreement between the measurement results on the developed method and the data of metallographic analysis is shown. [ABSTRACT FROM AUTHOR]

Copyright of Revista Ingeniería e Investigación is the property of Universidad Nacional de Colombia, Facultad de Ingenieraia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. In order for effective energy extraction from a solar PV system, this paper investigatesI–VandP–Vcharacteristics of solar PV modules and arrays. The paper particularly focuses onI–VandP–Vcharacteristics of PV modules and arrays under uneven shading conditions, and considers both the physics and electrical characteristics of a solar PV system in the model development. The article examines how different bypass diode arrangements could affect maximum power extraction characteristics of a solar PV module or array. It is found in this article that under uneven shading conditions, solar PV cells may perform in very different ways and a solar PV system may exhibit multiple peaks in itsP–Vcharacteristics. The study of this article also shows that the arrangement of largely distributed bypass diodes within a PV module could effectively improve efficiency and maximum power point tracking strategies for energy conversion of solar PV systems. [ABSTRACT FROM PUBLISHER]

This paper deals with 2-D simulation of GaAs MESFET, which includes velocity overshoot effects by using energy transport model suitable for submicron devices. Computation time is greatly reduced by simplifying the model and using fast convergence algorithms, e.g. Gummel interaction and ICCG method. The program shows good stability and convergence. Several types of GaAs MESFET structures, e.g., epitaxial ion-implanted and buried P-layer, have been simulated. The results show that buried P-layer can decrease carrier's injections into substrate and improve device performance. The results are also used to study carefully the velocity overshoot effects. By comparison of results of energy transport model and drift-diffusion model, the limitation of drift-diffusion-model is derived. [ABSTRACT FROM AUTHOR]

In this report, the diffusion of Zn, Zn−Cd in InGaAs is investigated using ZnAs and ZnAs+Cd as diffusion sources. The effect of the diffusion temperature, diffusion time, a variety of the diffusion source and composition x of the material on the relation of the ( X √ t) are given. The diffusion velocity X /t of Zn in InGaAs is faster than that of Zn−Cd in InGaAs, and at 500-600°C, the surface acceptor concentration is from 1×10 to 2×10 cm, which is higher than that of Zn in InP. Reduction of contact resistance by use of InGaAs contact layer for 1.3μm LED can be expected. [ABSTRACT FROM AUTHOR]

This paper reports some results in the investigation of deep levels in titanium diffusion-doped silicon; there Ti-related deep levels are observed by the DLTS. There are two elettron traps located at E −0.23 eV and E −0.53eV in n-Si(Ti) and a hole trap located at E +0.32eV in p-Si(Ti). Thermal activation energy and the capture cross-section in the range of experimental temperature and other related parameters for these traps are obtained by transient capacitance studies. Furthermore, from our experimental results, a brief discussion on the bonding feature of traps and on their pinning to which band is given. [ABSTRACT FROM AUTHOR]

In this article the development of an interactive tool for silicon semiconductor modeling is described. This tool includes four physical phenomena, two passive devices, and two active devices. We encourage the use of this tool in electronic physics lectures to help in the complete understanding of this phenomena and the associated devices. © 1998 John Wiley & Sons, Inc. Comput Appl Eng Educ 6: 59–65, 1998 [ABSTRACT FROM AUTHOR]

Substrate coupling in 3-D-ICs using Cu through silicon vias (TSVs) is a predicament widely documented in recent literature. Yet, discussions remain limited to the electromagnetic framework, such that a complete understanding of noise propagation and absorption is hampered. This letter thoroughly examines these phenomena in the TSVs from the integrated perspectives of semiconductor physics and electromagnetic theory and investigates the noise reduction method using the combination of p \(+\) guard-ring and grounded TSV via 3-D device simulation. [ABSTRACT FROM AUTHOR]

The electron spin is a natural two-level system that allows a qubit to be encoded. When localized in a gate-defined quantum dot, the electron spin provides a promising platform for a future functional quantum computer. The essential ingredient of any quantum computer is entanglement—for the case of electron-spin qubits considered here—commonly achieved via the exchange interaction. Nevertheless, there is an immense challenge as to how to scale the system up to include many qubits. In this paper, we propose a novel architecture of a large-scale quantum computer based on a realization of long-distance quantum gates between electron spins localized in quantum dots. The crucial ingredients of such a long-distance coupling are floating metallic gates that mediate electrostatic coupling over large distances. We show, both analytically and numerically, that distant electron spins in an array of quantum dots can be coupled selectively, with coupling strengths that are larger than the electron-spin decay and with switching times on the order of nanoseconds., Physics