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We propose a compact computational method based on the capacitance model for the efficient design of graphene-based synaptic field effect transistors (FETs), in which the hysteresis of conduction characteristics due to the channel–gate interface trap is used as synaptic plasticity. Using our method to calculate the conduction properties of graphene and armchair graphene nanoribbon (AGNR) superlattice FETs, it is shown that the AGNR can achieve an efficient conductance change rate Δ w , which is approximately 7.4 times that of graphene. It was also found that Δ w was the greatest when the gate oxide thickness was around 2–3 nm, which is near the limit of miniaturization. These results suggest that the proposed synaptic FETs are a promising approach to realize large scale integration chips for biological timescale computation. [ABSTRACT FROM AUTHOR]

GaxIn1−xAs–GaAsySb1−y type-II superlattices (T2SLs) have recently received broad attention as an InP-based optical absorption layer in short-wavelength infrared detectors. However, the cut-off wavelength of a GaInAs–GaAsSb T2SL detector is ordinarily around 2.4 µm at room temperature. This paper proposes extending the cut-off wavelength using a GaAs/InAs digital alloy instead of a GaxIn1-xAs random alloy layer in a GaxIn1−xAs–GaAsySb1−y T2SL. The calculation result employing an empirical sp3d5s* tight-binding method has revealed that a (GaAs/InAs)–GaAsySb1−y digital alloy T2SL on an InP substrate possesses a band gap corresponding to a wavelength of 2.9 µm which is over 0.4 µm longer than that in a conventional GaInAs–GaAsSb T2SL at a temperature of 200 K. Figured optical absorption coefficient spectra of certain digital alloy T2SLs, e.g., a [(GaAs)4(InAs)4]2–(GaAs0.53Sb0.47)17 structure, present a considerable polarization-direction dependence—originating from the asymmetrical shape of the wavefunction in the quantum well. Yet, by altering the atomic layer configuration in the growth direction of the digital alloy T2SL to have such a quantum well structure with a reflection symmetry as in [(GaAs)4(InAs)4]2(GaAs)3–(GaAs0.45Sb0.55)17, the polarization dependency can be dramatically decreased due to the symmetry improvement of the wavefunction. [ABSTRACT FROM AUTHOR]

We present a numerical study on the impact of electron–phonon scattering on the performance of a strained-graphene field-effect transistor, where the Dirac point of the channel region is shifted along the transverse momentum direction by a strain-induced vector potential and a high on-current/off-current (I on / I off ) ratio as well as a subthreshold slope (SS) steeper than 60 mV/dec have been predicted in the absence of the electron–phonon interaction previously. By using the Dirac-type effective Hamiltonian description for strained graphene and the non-equilibrium Green's function method to systematically account for the electron–phonon scattering, along with Poisson's equation, we demonstrate that the abovementioned I on / I off ratio and SS value can be maintained even in the presence of electron–phonon scattering, although the I on / I off ratio and the I D range over which the steep SS persists are reduced. [ABSTRACT FROM AUTHOR]

We have investigated the influence of nonparabolicity both of an imaginary band located in a bandgap and of a conduction band to improve the accuracy of energy levels for the design of GaInAs/AlInAs mid-infrared quantum cascade lasers (QCLs). The lasing wavelength of the QCL obtained experimentally was compared to that of the calculated optical gain peak by utilizing the single-band non-equilibrium Green's function (NEGF) method. We calculated the energy-dependent effective mass of electrons used in the NEGF calculation from the complex band structure of each bulk material forming the QCL. In a widely lasing wavelength range of 5–10 μm, the calculated gain peaks of the QCLs each agreed very well with the lasing wavelengths obtained experimentally. We have confirmed that in designing the QCL structures, energy dependency of the energy effective mass in the complex bands is significant. [ABSTRACT FROM AUTHOR]

We study the density of states (DOS) in a cylindrical quantum box formed by a cylindrical penetrable barrier and a planer penetrable double barrier perpendicular to the cylinder. The control of the cylindrical barrier thickness or height is found to cause the dimensional transitions from a three-dimensional (3D) DOS to a quasi-one-dimensional (Q1D) DOS and from a quasi-two-dimensional (Q2D) DOS to a quasi-zero-dimensional (QOD) DOS, if the strength of the planer double barrier is zero and infinity, respectively. In between the 3D and the Q1D (Q2D and QOD) limiting regimes, we found the presence of a Q2D (Q1D) like crossover regime. [ABSTRACT FROM AUTHOR]

We present an implementation study of gate-type quantum computing algorithms for the purpose of semiconductor device simulations. As one of the representative quantum algorithms we consider the use of HHL (Harrow–Hassidim–Lloyd) algorithm to solve the Poisson equation in semiconductor nanowire p–n junction under the Neumann boundary condition that the electric field is zero at the electrode boundaries. Our proposed model of the quantum gate to implement the Neumann boundary condition along with the appropriately designed non-uniform mesh grid has been found to successfully reproduce the solution obtained by conventional method. • An efficient quantum computing model to solve Poisson equation under Neumann boundary condition is proposed. • Non-uniform discretization are introduced so that adjacent eigenvalues of the capacitance matrix are separated as equally as possible. • Proposed scheme is found to reproduce accurate solution by a fewer resister qubits unless the charge profile is highly localized. [ABSTRACT FROM AUTHOR]

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO 2 , has been replaced by solid electrolytes, such as LiP 3 O 4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO 2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO 2 -gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li + ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability. [ABSTRACT FROM AUTHOR]

Abstract: We investigate numerically the effect of the interface structure on the spin-polarization of the electron transmission through zinc-blend semiconductor double barrier resonant tunneling heterostructures in which the well and barrier have a different composition of both anions and cations. Based on the atomistic tight binding model calculations including the intra-atomic spin–orbit interaction, it is demonstrated that the asymmetric configuration of the two barrier/well interfaces results in the strongly anisotropic spin-splitting of the transmission without use of the external electric field, where the interface asymmetry is interpreted to cause the additional effective spin–orbit coupling analogous to the Rashba spin–orbit coupling mechanism. [ABSTRACT FROM AUTHOR]

We study the ferromagnetism in III-V diluted magnetic semiconductor (DMS) quantum-wells theoretically and numerically taking into account the occupation of multiple subbands by holes in quantum wells. Starting from the mean-field theory of carrier-induced ferromagnetism in III-V DMS along with the exchange-correlation interaction of holes within the local spin density approximation, we found that the ferromagnetic transition temperature Tc of DMS quantum-wells exhibits step-function-like dependence on the hole density, reflecting the quasi-two-dimensional nature of systems. Moreover, the temperature dependence of the spin polarization shows quite distinct characteristics depending on the hole density. [ABSTRACT FROM AUTHOR]

Ferromagnetism in III–V diluted magnetic semiconductor (DMS) quantum wells is studied theoretically paying special attention to the occupation of multiple subbands by holes and the effect of static electric field perpendicular to the well plane. Our calculations show that the ferromagnetic transition temperature Tc of DMS quantum-well exhibits step-function-like dependence on the carrier concentration, reflecting the quasi-two-dimensional nature of systems. The Tc can be sensitively controlled by the application of electric field when the hole density is small so as to occupy only a few subbands. [Copyright &y& Elsevier]

Abstract: The formulation and calculation of quantum electron transport in double-gate metal oxide semi-conductor field effect transistors (DGMOSFETs) is presented based on multiband non-equilibrium Green''s function (NEGF) formalism. In the formulation we employ the empirical tight-binding approximation (TBA) with nearest neighbor coupling to obtain a realistic fullband structure. The multiband NEGF is performed self-consistently with the Poisson equation to acquire the effect of space charge density. We compare the non-parabolicity feature of bandstructure with that of parabolic effective mass model. Due to the difference in energy dispersion relation, we have found that the results of multiband simulations are quite different with those based on conventional effective mass model. [Copyright &y& Elsevier]

We study computationally the electronic transport properties through mechanically squashed zigzag carbon nanotubes (CNTs) under the uniform electric field perpendicular to the tube axis, based on the tight-binding molecular dynamics method for the structural analysis and the Landauer-Büttiker's formalism for the transport analysis. Our simulations show that the band gaps of the zigzag carbon nanotubes exhibit nonlinear decrease as increasing the deformation ratio in the presence of the external perpendicular electric field, in contrast to the case of zero electric field, where the band gap decreases linearly as increasing the deformation ratio. Such properties allow us to tune the sensitivity of the electromechanical response in CNT devices by applying the external electric field. [ABSTRACT FROM AUTHOR]

We evaluate analytically and numerically the density of states (DOS) and the heat capacity in a spherical quantum dot formed by a spherical thin barrier. The control of the spherical barrier thickness or the potential barrier height is found to cause the dimensional transition from the three-dimensional (3D) behavior to the quasi-zero dimensional (Q0D) behavior in the DOS and the heat capacity. When the barrier is thick enough, the DOS shows the Q0D-like behavior but when the barrier is thin enough to allow electrons to tunnel through it, the temperature dependence of the heat capacity exhibits quite a distinct behavior depending on the electron density. Explicit numerical plots are given in the low density regime. [ABSTRACT FROM AUTHOR]

Abstract: We present a theoretical study of the density of states (DOS) and the heat capacity in a spherical quantum dot formed by a spherical thin barrier. The control of the spherical barrier thickness or the potential barrier height is found to cause the dimensional transition from the three-dimensional (3D) behavior to the quasi-zero dimensional (Q0D) behavior in the DOS and the heat capacity. When the barrier is thick enough the DOS shows the Q0D-like behavior but when the barrier is thin enough to allow electrons to tunnel through it, the temperature dependence of the heat capacity exhibits quite distinct behavior depending on the electron density. [Copyright &y& Elsevier]