arXiv subjects

Nobuyuki Sano

Publications and source records attributed to Nobuyuki Sano.

3 recordsLinked to original sources

arXiv2026

Microscopic Modeling of Surface Roughness Scattering in Inversion Layers of MOSFETs Based on Ando's Linear Model

Surface roughness (SR) scattering in inversion layers of bulk-MOSFETs is studied from the atomistic and quantum-mechanical viewpoints. Contrary to the usual macroscopic landscape of the roughness deviation, we introduce a stochastic deviation at each atomic site to take account of the discontinuity of the spatial derivatives of the electrostatic potential and wave-function at the semiconductor/dielectric interface, leading to an ambiguity in roughness positions. It is shown that SR parameters are consistent with those known from the experiments and, thus, there is no discrepancy problem associated with the roughness parameters in our model. The self-consistent scattering rate is derived under the framework of the Green's functions scheme: We find that the SR scattering rates are intrinsically nonlocal (non-diagonal) with respect to subband indices and greatly deviate from those based on Fermi's golden rule in the regimes of strong effective fields and/or low electron energies. As a result, the conventional SR model tends to underestimate the surface-roughness-limited mobility.

cond-mat.mes-hall↗

arXiv2025

Nonequilibrium Green's Function Formalism Applicable to Discrete Impurities in Semiconductor Nanostructures

A new theoretical framework for the nonequilibrium Green's function (NEGF) scheme is presented to account for the discrete nature of impurities doped in semiconductor nanostructures. The short-range part of impurity potential is included as scattering potential in the self-energy due to spatially localized impurity scattering, and the long-range part of impurity potential is treated as the self-consistent Hartree potential by coupling with the Poisson equation. The position-dependent impurity scattering rate under inhomogeneous impurity profiles is systematically derived so that its physical meaning is clarified. The position dependence of the scattering rate turns out to be represented by the `center of mass' coordinates in the Wigner coordinates, rather than the real-space coordinates. Consequently, impurity scattering is intrinsically nonlocal in space. The proposed framework is applied to cylindrical thin wires under the quasi-one-dimensional (quasi-1D) approximation. We show explicitly how the discrete nature of impurities affects the transport properties such as electrostatic potential, local density of states, carrier density, scattering rates, and mobility.

cond-mat.mes-hall↗

arXiv2021

Quantum Kinetic Equation for the Wigner Equation and Reduction to the Boltzmann Transport Equation under Discrete Impurities

We drive a quantum kinetic equation under discrete impurities for the Wigner function from the quantum Liouville equation. To attain this goal, the electrostatic Coulomb potential is separated into the long- and short-range parts, and the self-consistent coupling with Poisson's equation is explicitly taken into account. It is shown that the collision integral associated with impurity scattering as well as the usual drift term is derived on an equal footing and that the conventional treatment of impurity scattering under the Wigner function scheme is inconsistent in the sense that the collision integral is introduced in an ad hoc way and, thus, the short-range part of the impurity potential is double-counted. The Boltzmann transport equation (BTE) is derived without imposing an assumption of random impurity configurations over the substrate. The derived BTE is able to describe the discrete nature of impurities such as potential fluctuations and, thus, appropriate to analyze electron transport under semiconductor nanostructures.

cond-mat.mes-hall↗