arXiv subjects

Raúl Rengel

Publications and source records attributed to Raúl Rengel.

4 recordsLinked to original sources

arXiv2019

Radio frequency performance projection and stability trade-off of h-BN encapsulated graphene field-effect transistors

Hexagonal boron nitride (h-BN) encapsulation significantly improves carrier transport in graphene. This work investigates the benefit of implementing the encapsulation technique in graphene field-effect transistors (GFET) in terms of their radio frequency (RF) performance. For such a purpose, a drift-diffusion self-consistent simulator is prepared to get the GFET electrical characteristics. Both the mobility and saturation velocity information are obtained by means of an ensemble Monte Carlo simulator upon considering the relevant scattering mechanisms that affect carrier transport. RF figures of merit are simulated using an accurate small-signal model that includes non-reciprocal capacitances. Results reveal that the cutoff frequency could scale up to the physical limit given by the inverse of the transit time. Projected maximum oscillation frequencies, in the order of few THz, are expected to exceed the values demonstrated by InP and Si based RF transistors. The existing trade-off between power gain and stability and the role played by the gate resistance are also studied. High power gain and stability are feasible even if the device is operated far away from current saturation. Finally, the benefits of device unilateralization and the exploitation of the negative differential resistance region to get negative-resistance gain are discussed.

cond-mat.mes-hall↗

arXiv2017

Scaling of graphene field-effect transistors supported on hexagonal boron nitride: radio-frequency stability as a limiting factor

The quality of graphene in nanodevices has increased hugely thanks to the use of hexagonal boron nitride as a supporting layer. This paper studies to which extent hBN together with channel length scaling can be exploited in graphene field effect transistors (GFETs) to get a competitive radio frequency (RF) performance. Carrier mobility and saturation velocity were obtained from an ensemble Monte Carlo simulator that accounted for the relevant scattering mechanisms (intrinsic phonons, scattering with impurities and defects, etc.). This information is fed into a self consistent simulator, which solves the drift diffusion equation coupled with the two dimensional Poisson's equation to take full account of short channel effects. Simulated GFET characteristics were benchmarked against experimental data from our fabricated devices. Our simulations show that scalability is supposed to bring to RF performance an improvement that is, however, highly limited by instability. Despite the possibility of a lower performance, a careful choice of the bias point can avoid instability. Nevertheless, maximum oscillation frequencies are still achievable in the THz region for channel lengths of a few hundreds of nanometers.

physics.app-ph↗

arXiv2016

Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene

We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared to considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between $1$ and $3\times 10^{12} \mathrm{~cm}^{-2}$. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.

cond-mat.mes-hall↗

arXiv2014

Influence of the substrate on the diffusion coefficient and the momentum relaxation in graphene: the role of surface polar phonons

Knowing the influence of the substrate type on the diffusion coefficient and the momentum relaxation in graphene is of great importance for the development of new device models specifically adapted to the peculiarities of this material. In this work, the influence of surface polar phonons at low and high electric fields is evaluated by means of ensemble Monte Carlo simulations for several types of substrates. The results show that at low fields surface polar phonons have a major role on reducing the scattering time, breaking the correlation of velocity fluctuations and degrading the diffusion coefficient. At high fields the differences with regard to suspended samples in terms of diffusivity and momentum relaxation tend to reduce, providing at the same time larger saturation velocities, particularly for h-BN.

cond-mat.mes-hall↗