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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 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]