Effect of discrete impurities on electron transport in ultra-short MOSFET using 3D Monte Carlo simulation

This paper discusses the influence of the channel impurity distribution on the transport and the drive current in short-gate MOSFET. In this purpose, a careful description of electron-ion interaction suitable for the case of discrete impurities has been implemented in a 3D particle Monte Carlo simulator. This transport model is applied to the investigation of 50 nm MOSFET operation. The results show that a small change in the number of doping impurities or in the position of a single discrete impurity in the inversion layer may significantly influence the drain current. This effect is not only related to threshold voltage fluctuations but also to variations in transport properties in the inversion layer, especially at high drain voltage. The results are analyzed in terms of local fluctuations of electron velocity and current density. In a set of fifteen simulated devices the drive current Ion, determined at VGS = VDS = 0.6 V, is found to vary in a range of 23% according to the position of channel impurities.Comment: 31 pages, 13 figures, revised version: discussions and references added, to be published in IEEE Trans. Electron. Device

Scaling Law in Carbon Nanotube Electromechanical Devices

We report a method for probing electromechanical properties of multiwalled carbon nanotubes(CNTs). This method is based on AFM measurements on a doubly clamped suspended CNT electrostatically deflected by a gate electrode. We measure the maximum deflection as a function of the applied gate voltage. Data from different CNTs scale into an universal curve within the experimental accuracy, in agreement with a continuum model prediction. This method and the general validity of the scaling law constitute a very useful tool for designing actuators and in general conducting nanowire-based NEMS.Comment: 12 pages, 4 figures. To be published in Phys. Rev. Let

Gate-induced spin precession in an In

We report a study of the gate-induced spin precession in an In0.53Ga0.47As two dimensional electron gas, using a Monte-Carlo transport model. The precession vector originates from the spin-orbit coupling existing at a III-V hetero-interface, usually denoted as Rashba interaction. Contrary to the case of a one dimensional electron gas, the precession vector is randomized by the scattering events, which leads to a non negligible loss of spin coherence for an initially spin-polarized electron population moving along a conduction channel. However, we show that by operating at the liquid nitrogen temperature, or by reducing the channel width to a value close to 0.1 µm, the gate-controlled spin-polarization remains high enough to enable the investigation of the physics of spin-related phenomena in a ferromagnet/semiconductor structure

Monte Carlo simulation of pseudomorphic InGaAs/GaAs high electron mobility transistors: Physical limitations at ultrashort gate length

International audienceUsing Monte Carlo simulations, we study pseudomorphic uniformly doped AlGaAs/InGaAs/GaAs high electron mobility transistors with very short gate lengths (150 and 50 nm). In open‐channel range of operation the saturation of the rain current is ensured by the existence of a pseudodipolar domain between the gate and the drain where the increase in drain potential is dropped. We describe the short channel effects, such as the high drain conductance, that occur in the pinchoff range of operation (especially in the shortest device). In this case the overheated electrons can easily transfer to the upper large band gap layer and cannot form any domain. The potential barrier that controls the current is gradually lowered by the drain potential increase, which is favoring the electron injection from the source side. Short channel effects are also involved in the relatively weak transconductance obtained in the 50 nm gate device, gm=800 mS/mm, to be compared with 900 mS/mm reached in a 150 nm gate device. Finally, we show that the occurring of short channel effects can be predicted from very simple one‐dimensional calculations along two perpendicular directions of the device, by taking into account the lateral diffusion from the source access zone to the active zone

Monte Carlo study of 50 nm-long single and dual-gate MODFETs: suppression of short-channel effects

A theoretical study of 50 nm-Single and Dual-Gate MODFETs using Monte Carlo simulation is reported. The introduction of a second gate, whose potential is fixed to a positive value, between the control-gate and the drain allows to efficiently provide against short-channel effects that occur in ultra-short single-gate MODFET. We describe the physical operating of these devices and especially the role of the second gate. The dual-gate MODFET exhibits an excellent saturation behaviour compared with single-gate MODFETs together with high values of transconductance $g_{\rm m}$ and current gain cutoff frequency $f_{\rm T}$. This is resulting in a large improvement in the $g_{\rm m}$ to $g_{\rm D}$, ratio.Nous présentons une étude théorique, à partir de simulations Monte Carlo, de MODFETs à simple et double grille de 50 nm de longueur. L'introduction d'une seconde grille située entre la grille de commande et le drain et dont le potentiel est fixé à une valeur positive permet de s'affranchir des effets de canal court qui apparaissent dans les MODFETs à très courte longueur de grille. Nous décrivons le fonctionnement physique de ces dispositifs et en particulier le rôle de la seconde grille. Le MODFET bi-grille présente d'excellentes caractéristiques de drain en saturation tout en offrant des valeurs élevées de transconductance $g_{\rm m}$ et de fréquence de coupure $f_{\rm T}$. Il en résulte une amélioration importante du rapport $g_{\rm m}/g_{\rm D}$

Réalisation et modélisation Monte-Carlo du Transistor Bipolaire à Hétérojonctions NnpnN InGaAlAs/InGaAs/InGaAlAs

Ce papier présente une étude expérimentale et une analyse par simulation Monte-Carlo de Transistors Bipolaires à Hétérojonctions InGaAlAs/InGaAs/InGaAlAs avec et sans espaceurs. Ces espaceurs, destinés à séparer les jonctions électriques et métallurgiques, permettent de diminuer les hauteurs de barrière vues par les électrons tout en conservant celles vues par les trous. L'injection, de nature thermoïonique pour les hétérojonctions abruptes, se fait par effet diffusif lorsque l'on introduit un espaceur, et ainsi le coefficient d'injection est augmenté. D'autre part les espaceurs au collecteur conduisent à une meilleure collection des électrons, cette collection étant facilitée par une injection d'électrons chauds dans le cas d'une hétéro jonction émetteur-base abrupte. Les gains en courant en émetteur commun obtenus sont supérieurs à 100

UNIDIMENSIONAL PARTICULE MODEL OF CONDUCTION IN N TYPE GaAs AT LOW TEMPERATURE : CONTACTS INFLUENCE

Nous décrivons un modèle particulaire unidimensionnel utilisé pour modéliser la conduction électronique dans une couche de 4000 Å d'AsGa de type N à 77 K. Nous envisageons différentes conditions d'injection, présentons les résultats obtenus et proposons une caractérisation possible du transport balistique.We discribe a unidimensional particle model of electronic conduction in a 4000 Å N type layer of GaAs at 77 K. We study the contact influence, show some results and propose a possible characterisation of the ballistic transport

Monte-Carlo investigation of in-plane electron transport in tensile strained Si and Si

Electron transport properties in tensile strained Si-based materials are theoretically analyzed using Monte-Carlo calculation. We focus our interest on in-plane transport in Si and Si1−yCy (y ≤ 0.03), grown respectively on 〈001〉 Si1−xGex pseudo-substrate and Si substrate, with a view to Field-Effect-Transistor application. In comparison with unstrained Si, the tensile strain effect is shown to be very attractive in Si: drift mobilities greater than 3000 cm2/Vs are obtained at 300 K for a Ge fraction mole of 0.2 in the pseudo-substrate. In the Si1−yCy/Si system, that does not need any pseudo-substrate, the beneficial strain effect on transport is counterbalanced by the alloy scattering whose influence on mobility is studied. If the alloy potential is greater than about 1 eV, the advantage of strain-induced reduction of effective mass is lost in terms of stationary transport performance at 300 K

High frequency analysis of fast devices using small-signal Monte Carlo simulations : application to a 0.1 μ\mum-gate MODFET

A method of small signal analysis of fast devices using Monte Carlo simulations is presented. It consists in expanding the terminal currents and voltages in Fourier series. It allows to determine the current gain cutoff frequency and to extract the parameters of an equivalent circuit. This method is applied to a 0.1 $\mu$m-gate AlGaAs/InGaAs/GaAs MODFET.Nous présentons une méthode d'analyse petits signaux de composants rapides à partir de simulations Monte Carlo. Elle consiste à développer en séries de Fourier les tensions et courants aux électrodes. Elle permet de déterminer la fréquence de coupure du gain en courant et d'extraire les paramètres d'un schéma équivalent. Cette méthode est appliquée à un MODFET AlGaAs/InGaAs/GaAs de longueur de grille 0,1 $\mu$m