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IS THE REGIME WITH SHOT NOISE SUPPRESSION BY A FACTOR 1/3 ACHIEVABLE IN SEMICONDUCTOR DEVICES WITH MESOSCOPIC DIMENSIONS?

We discuss the possibility of diffusive conduction and thus of suppression of shot noise by a factor 1/3 in mesoscopic semiconductor devices with two-dimensional and one-dimensional potential disorder, for which existing experimental data do not provide a conclusive result. On the basis of our numerical analysis, we conclude that it is quite difficult to achieve diffusive transport over a reasonably wide parameter range, unless the device dimensions are increased up to the macroscopic scale where, however, shot noise disappears because the device length exceeds the Debye length. In addition, in the case of one-dimensional disorder, some mechanism capable of mode-mixing has to be present in order to reach or even approach the diffusive regime.

High-performance solution of the transport problem in a graphene armchair structure with a generic potential.

We propose an efficient numerical method to study the transport properties of armchair graphene ribbons in the presence of a generic external potential. The method is based on a continuum envelope-function description with physical boundary conditions. The envelope functions are computed in the reciprocal space, and the transmission is then obtained with a recursive scattering matrix approach. This allows a significant reduction of the computational time with respect to finite difference simulations.

Sinc-based method for an efficient solution in the direct space of quantum wave equations with periodic boundary conditions

The solution of differential problems, and in particular of quantum wave equations, can in general be performed both in the direct and in the reciprocal space. However, to achieve the same accuracy, direct-space finite-difference approaches usually involve handling larger algebraic problems with respect to the approaches based on the Fourier transform in reciprocal space. This is the result of the errors that direct-space discretization formulas introduce into the treatment of derivatives. Here, we propose an approach, relying on a set of sinc-based functions, that allows us to achieve an exact representation of the derivatives in the direct space and that is equivalent to the solution in the reciprocal space. We apply this method to the numerical solution of the Dirac equation in an armchair graphene nanoribbon with a potential varying only in the transverse direction.

Operation and Design of van der Waals Tunnel Transistors: A 3-D Quantum Transport Study

We propose a model Hamiltonian for van der Waals tunnel transistors (vdW-TFETs) relying on few physical parameters calibrated against density functional theory (DFT) band structure calculations. Based on this model, we develop a fully 3-D nonequilibrium Greens function simulator including electron-phonon scattering, and we investigate some fundamental aspects and design challenges related to vdW-TFETs based on single-layer MoS2 and WTe2. In particular, we devote a specific analysis to the impact of top gate alignment and back-oxide thickness on the device performance. Our results suggest that the vdW-TFETs can provide very small values of subthreshold swing (SS) and fairly good ON-state current. However, these devices also pose specific design challenges related to the geometrical features of gated regions, and their ultimate SS may be lower limited by inelastic phonon scattering.

A computational study of van der Waals tunnel transistors: Fundamental aspects and design challenges

We propose a model Hamiltonian for van der Waals tunnel transistors relying on a few physical parameters that we calibrate against DFT band structure calculations. This approach allowed us to develop a fully three-dimensional (3-D) NEGF based simulator and to investigate fundamental and design aspects related to van der Waals tunnel transistors, such as: (a) area and edge tunneling components, and scaling with device area; (b) impact of top gate alignment and back-oxide thickness on the device performance; (c) influence of inelastic phonon scattering on the device operation and sub-threshold swing; (d) benchmarking of switching energy and delay.

Using gate voltages to tune the noise properties of a mesoscopic cavity

We propose a layout for a tunable mesoscopic cavity that allows to probe the conductance and noise properties of direct transmission channels (“noiseless scattering states”). Our numerical simulations demonstrate how the variation of different gate voltages in the cavity leads to characteristic signatures of such non‐universal processes. Using realistic assumptions about scattering in two‐dimensional heterostructures, our proposed layout should define a viable protocol for an experimental realization.