Elena Pascual

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.

Injected Current and Quantum Transmission Coefficient in Low Schottky Barriers: WKB and Airy Approaches

An exact solution of the quantum transmission coefficient has been obtained by using an Airy-transfer-matrix formalism to solve Schroumldinger equation. The procedure is applied to the calculation of the transmission coefficient in reverse-biased low Schottky diodes. The barrier profiles are given by Monte Carlo device simulations. As compared to the exact calculation, results indicate that injected current is much exacerbated when considering Wentzel-Kramers-Brillouin (WKB) approach or when neglecting quantum mechanical reflections for energies over the potential barrier. However, WKB could reasonably predict the total current if properly modifying the model parameters. Influence of barrier lowering is also discussed

Enhanced carrier injection in Schottky contacts using dopant segregation: a Monte Carlo research

In this paper we present a Monte Carlo research of the impact, on carrier transport, of including a dopant-segregated layer adjacent to the Schottky contact in back-to-back diodes. A comparison with a homogeneous structure is developed, evidencing that the doped layer boosts the tunneling current through the Schottky barrier, thus significantly improving the injection of carriers at the contact. We have carried out a complete study of carrier injection and transport in the region close to the reverse-biased contact together with the analysis of internal quantities such as conduction band, carrier density and electric field. The effect of temperature on the current is also evaluated. The study of the velocity distribution functions and the average number of scatterings undergone by the carriers reveals that devices with dopant segregation exhibit an enhancement of the ballistic transport in the first nanometers close to the Schottky contact.

Microscopic modelling of reverse biased Schottky diodes : influence of non-equilibrium transport phenomena

A Monte Carlo investigation of charge transport—including quantum tunnelling effects—across Schottky barriers (both n-type and p-type) in the reverse bias regime is presented. The effect of the variation of different quantities (such as the barrier height or the temperature) over the current density is discussed and extensively analysed. A thorough study of different internal magnitudes such as carrier density, electric field, etc. together with velocity distribution functions and the density of scattering mechanisms has been carried out. In this way, a detailed description of microscopic charge transport in the depletion region associated with the Schottky contact is attained. Results evidence important quasi-ballistic characteristics in the region closer to the contact, thus becoming an important issue to be tackled in the modelling of Schottky-based devices with reverse biased junctions.

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

Monte Carlo Study of Dopant-Segregated Schottky Barrier SoI MOSFETs: Enhancement of the RF Performance

1

Current drive in n-type Schottky Barrier MOSFETs: a Monte Carlo study

and

Noise temperature in graphene at high frequencies

3\times 10^{12} \mathrm{~cm}^{-2}

Carrier-carrier and carrier-phonon interactions in the dynamics of photoexcited electrons in graphene

. 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.

Spectral density of velocity fluctuations under switching field conditions in graphene

This paper presents a detailed Monte Carlo study of the optimization of the dopant segregation (DS) layer in n-type Schottky barrier (SB)-MOSFET. It is shown that with a careful control of the DS layer parameters, dopant concentration (Ndop), and length (Ldop), the performance of the devices is significantly enhanced. The presence of the DS layer induces crucial effects in the injection processes at the Schottky contacts. The benefits of increasing the length and the doping level of the DS layer are studied from the microscopic point of view (transit times, average number of scatterings). The effect of varying these parameters is also analyzed through the nonquasi-static parameters of the small signal equivalent circuit, which can be useful for designers to improve the reliability of the SB-MOSFET technology.