Analytical model of 1D Carbon-based Schottky-Barrier Transistors

Nanotransistors typically operate in far-from-equilibrium (FFE) conditions, that cannot be described neither by drift-diffusion, nor by purely ballistic models. In carbonbased nanotransistors, source and drain contacts are often characterized by the formation of Schottky Barriers (SBs), with strong influence on transport. Here we present a model for onedimensional field-effect transistors (FETs), taking into account on equal footing both SB contacts and FFE transport regime. Intermediate transport is introduced within the Buttiker probe approach to dissipative transport, in which a non-ballistic transistor is seen as a suitable series of individually ballistic channels. Our model permits the study of the interplay of SBs and ambipolar FFE transport, and in particular of the transition between SB-limited and dissipation-limited transport

Analytical model of nanowire FETs in a partially ballistic or dissipative transport regime

The intermediate transport regime in nanoscale transistors between the fully ballistic case and the quasi equilibrium case described by the drift-diffusion model is still an open modeling issue. Analytical approaches to the problem have been proposed, based on the introduction of a backscattering coefficient, or numerical approaches consisting in the MonteCarlo solution of the Boltzmann transport equation or in the introduction of dissipation in quantum transport descriptions. In this paper we propose a very simple analytical model to seamlessly cover the whole range of transport regimes in generic quasi-one dimensional field-effect transistors, and apply it to silicon nanowire transistors. The model is based on describing a generic transistor as a chain of ballistic nanowire transistors in series, or as the series of a ballistic transistor and a drift-diffusion transistor operating in the triode region. As an additional result, we find a relation between the mobility and the mean free path, that has deep consequences on the understanding of transport in nanoscale devices

Electric-Field-control of spin rotation in bilayer graphene

The manipulation of the electron spin degree of freedom is at the core of the spintronics paradigm, which offers the perspective of reduced power consumption, enabled by the decoupling of information processing from net charge transfer. Spintronics also offers the possibility of devising hybrid devices able to perform logic, communication, and storage operations. Graphene, with its potentially long spin-coherence length, is a promising material for spin-encoded information transport. However, the small spin-orbit interaction is also a limitation for the design of conventional devices based on the canonical Datta-Das spin-FET. An alternative solution can be found in magnetic doping of graphene, or, as discussed in the present work, in exploiting the proximity effect between graphene and Ferromagnetic Oxides (FOs). Graphene in proximity to FO experiences an exchange proximity interaction (EPI), that acts as an effective Zeeman field for electrons in graphene, inducing a spin precession around the magnetization axis of the FO. Here we show that in an appropriately designed double-gate field-effect transistor, with a bilayer graphene channel and FO used as a gate dielectric, spin-precession of carriers can be turned ON and OFF with the application of a differential voltage to the gates. This feature is directly probed in the spin-resolved conductance of the bilayer

Model and performance evaluation of field-effect transistors based on epitaxial graphene on SiC

In view of the appreciable semiconducting gap of 0.26 eV observed in recent experiments, epitaxial graphene on a SiC substrate seems a promising channel material for FETs. Indeed, it is two-dimensional - and therefore does not require prohibitive lithography - and exhibits a wider gap than other alternative options, such as bilayer graphene. Here we propose a model and assess the achievable performance of a nanoscale FET based on epitaxial graphene on SiC, conducting an exploration of the design parameter space. We show that the current can be modulated by 4 orders of magnitude; for digital applications an Ion /Ioff ratio of 50 and a subthreshold slope of 145 mV/decade can be obtained with a supply voltage of 0.25 V. This represents a significant progress towards solid-state integration of graphene electronics, but not yet sufficient for digital applications

Model of tunneling transistors based on graphene on SiC

Recent experiments shown that graphene epitaxially grown on Silicon Carbide (SiC) can exhibit a energy gap of 0.26 eV, making it a promising material for electronics. With an accurate model, we explore the design parameter space for a fully ballistic graphene-on-SiC Tunnel Field-Effect Transistors (TFETs), and assess the DC and high frequency figures of merit. The steep subthreshold behavior can enable I_{ON}/I_{OFF} ratios exceeding 10^4 even with a low supply voltage of 0.15 V, for devices with gatelength down to 30 nm. Intrinsic transistor delays smaller than 1 ps are obtained. These factors make the device an interesting candidate for low-power nanoelectronics beyond CMOS

Exciton-phonon scattering and photo-excitation dynamics in J-aggregate microcavities

We have developed a model accounting for the photo-excitation dynamics and the photoluminescence of strongly coupled J-aggregate microcavities. Our model is based on a description of the J-aggregate film as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. In a strongly coupled microcavity exciton-polaritons are formed, mixing superradiant excitons and cavity photons. The calculation of the microcavity steady-state photoluminescence, following a CW non resonant pumping, is carried out. The experimental photoluminescence intensity ratio between upper and lower polariton branches is accurately reproduced. In particular both thermal activation of the photoluminescence intensity ratio and its Rabi splitting dependence are a consequence of the bottleneck in the relaxation, occurring at the bottom of the excitonic reservoir. The effects due to radiative channels of decay of excitons and to the presence of a paritticular set of discrete optical molecular vibrations active in relaxation processes are investigared.Comment: 8 pages, 6 figure