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oral; National audience

[EN]III-V Impact-ionization (II) metal-oxide-semiconductor FETs (I-MOSFETs) and tunnel FETs (TFETs) are being explored as promising devices for low-power digital applications. To assist the development of these devices from the physical point of view, a Monte Carlo (MC) model which includes impact ionization processes and band-to-band tunneling is presented. The MC simulator reproduces the I-V characteristics of experimental ungated In0.53Ga0.47As 100 nm PIN diodes, in which tunneling emerges for lower applied voltages than impact ionization events, thus being appropriate for TFETs. When the structure is enlarged up to 200 nm, the ON-state is achieved by means of impact ionization processes; however, the necessary applied voltage is higher, with the consequent drawback for low-power applications. In InAs PIN ungated structures, the onset of both impact ionization processes and band-to-band tunneling takes place for similar applied voltages, lower than 1V; thus they are suitable for the design of low-power I-MOSFETs.

The frequency response of nanometric T- and Y-shaped three-terminal junctions (TTJs) is investigated experimentally and numerically. In virtue of the parabolic down-bending of the output voltage of the central branch obtained at room temperature under a push-pull fashion input, we analyze: the low-frequency performance (, ROOTHz (FP7-243845)

Se han estudiado las características estáticas y dinámicas de HEMTs de doblre puerta (DG-HEMTs) por medio de simulaciones Monte Carlo, y se han comparado con las de los HEMTs de puerta única. Las simulaciones reproducen adecuadamente los resultados experimentales y permiten confirmar y explicar desde el punto de vista microscópico el origen de la reducción de los efectos de canal corto y el aumento de fmax que se observa en los transistores de doble puerta., The static and dynamic behavior of InAlAs/InGaAsdouble-gate high-electron mobility transistors (DG-HEMTs) isstudied by means of an ensemble 2-D Monte Carlo simulator.The model allows us to satisfactorily reproduce the experimentalperformance of this novel device and to go deeply into its physicalbehavior. A complete comparison between DG and similarstandard HEMTs has been performed, and devices with differentgate lengths have been analyzed in order to check the attenuationof short-channel effects expected in the DG-structures. Wehave confirmed that, for very small gate lengths, short-channeleffects are less significant in the DG-HEMTs, leading to a betterintrinsic dynamic performance. Moreover, the higher values ofthe transconductance over drain conductance ratio gm/gd and,especially, the lower gate resistance Rg also provide a significantimprovement of the extrinsic fmax.

Segunda parte del estudio basado en simulaciones Monte Carlo de HEMTs de InGaAs con 50nm de longitud de puerta. En este caso se estudia el efecto sobre el ruido del nivel de dopaje delta, de la anchura de los transistores y también de la longitud del recess. El efecto sobre el ruido del dopaje delta y de la anchura es similar al que tienen sobre ft y fmax, deteriorándose al elevar ambos. Además, hemos confirmado que la reducción de la longitud del recess tiene un efecto beneficioso sobre el ruido de los HEMTs., In order to optimize the low-noise performance of 50-nm-gate AlInAs/GaInAs HEMTs, by using an ensemble Monte Carlo simulation we study the influence of three important technological parameters on their noise level: the doping of the ?-doped layer, the width of the devices and the length of the recess. The noise behavior of the devices is firstlyanalyzed in terms of the physics-based P, R and C parameters, and then characterized from a practical (circuit oriented) point of view through their four noise parameters: minimum noise figure, Fmin, noise resistance, Rn, and complex input admittance, Yopt (or reflection coefficient, ?opt). We have observed an enhancement of the noise when the??doping or the device width are increased (a deterioration parallel to that of fmax).Thus, the optimum noise operation is obtained for the lowest possible values of the ??doping and device width. However, for small width the effect of the offset parasitic capacitances makes Fmin increase, thus imposing a limit for the reduction of the noise.Moreover, the increase of Rn for small W makes the noise tuning condition critical to reach the optimum low-noise operation. We have also confirmed that when shortening the recess length from 100 nm to 20 nm at each side of the gate Fmin is reduced, with a slight deterioration of fmax, while the static characteristics are not modified.

Por medio de simulaciones Monte Carlo se ha estudiado el efecto que tienen sobre las características dinamicas de HEMTs de InGaAs con 50nm de longitud de puerta dos parámetros importantes en la fabricación de los transistores: su anchura y el nivel de dopaje de la capa delta. El cálculo de los valores de las frecuencias de corte ft y fmax nos ha permitido concluir que el dopaje delta debe ser lo menor posible para mejorar las prestaciones en alta frecuencia, con el problema que tanbien hace disminuir la potencia entregada. También la anchura de los transistores debe ser la menor posible para obtener valores óptimos de ft y fmax, siempre teneiendo en cuenta que al reducirla el efecto de las capacidades puede hacerse importante., By using a Monte Carlo simulator, the static and dynamic characteristics of 50-nm-gate AlInAs GaInAs -dopedhigh-electron mobility transistors (HEMTs) are investigated. The Monte Carlo model includes some important effects that areindispensable when trying to reproduce the real behavior of the devices, such as degeneracy, presence of surface charges, T-shape of the gate, presence of dielectrics, and contact resistances. Among the large quantity of design parameters that enter the fabricationof the devices, we have studied the influence on their performanceof two important factors: the doping level of the -doped layer, and the width of the devices. We have confirmed that the value of the -doping must be increased to avoid the reduction of the drain current due to the depletion of the channel by the surface potential.However, a higher -doping has the drawback that the frequency performance of the HEMTs is deteriorated, and its value must be carefully chosen depending on the system requirements in termsof delivered power and frequency of operation. The reduction of the device width has been also checked to improve the cutoff frequencies of the HEMTs, with a lower limit imposed by the degradation provoked by the offset extrinsic capacitances.

Estudio sobre dispositivos balísticos, [ES]Mediante un simulador Monte Carlo semiclásico 2D se analizan dispositivos balísticos nanométricos basados en canales de AlInAs/InGaAs. Los resultados de las simulaciones reproducen cualitativamente las medidas experimentales realizadas en uniones en T y en Y, así como en rectificadores de cuatro terminales, cuyo comportamiento se basa en la presencia de transporte balístico. Se demuestra que para explicar el origen físico de estos efectos no es precisa una descripción cuántica, ya que la coherencia de fase no juega un papel esencial en su funcionamiento., [EN]By using a semi-classical two-dimensional (2-D) Monte Carlo simulation, simple ballistic devices based on AlInAs/InGaAs channels are analyzed. Our simulations qualitativelyreproduce the experimental results in T- and Y-branch junctions as well as in a ballistic rectifier appearing as a result ofelectron ballistic transport. We show that a quantum description of electron transport is not essential for the physical explanation of these results since phase coherence plays no significant role.On the contrary, its origin can be purely classical: the presence ofclassical electron transport and space charge inside the structures.