Quasi-ballistic Transport Model Research Articles

Mobility and quasi-ballistic charge carrier transport in graphene field-effect transistors

The optimization of graphene field-effect transistors (GFETs) for high-frequency applications requires further understanding of the physical mechanisms concerning charge carrier transport at short channel lengths. Here, we study the charge carrier transport in GFETs with gate lengths ranging from 2 μm down to 0.2 μm by applying a quasi-ballistic transport model. It is found that the carrier mobility, evaluated via the drain–source resistance model, including the geometrical magnetoresistance effect, is more than halved with decreasing the gate length in the studied range. This decrease in mobility is explained by the impact of ballistic charge carrier transport. The analysis allows for evaluation of the characteristic length, a parameter of the order of the mean-free path, which is found to be in the range of 359–374 nm. The mobility term associated with scattering mechanisms is found to be up to 4456 cm2/Vs. Transmission formalism treating the electrons as purely classical particles allows for the estimation of the probability of charge carrier transport without scattering events. It is shown that at the gate length of 2 μm, approximately 20% of the charge carriers are moving without scattering, while at the gate length of 0.2 μm, this number increases to above 60%.

Quasi-ballistic transport model for nanoscale MOSFETs: learnings from a diffusive conductor

The fundamental understanding of transport in ballistic transistors is an important area of research since modern transistors have channel lengths that approach the mean scattering length of carriers. Here, we provide a systematic approach to developing a quasi-ballistic transport model of highly scaled transistors, with only a few fitting parameters. These parameters are physical and follow naturally from the underlying physics of transport in ballistic conductors. Beginning with the band diagram of a diffusive conductor, we show how the number of fitting parameters evolves for describing a quasi-ballistic transistor. To support our model, we benchmark it against a wide range of nanoscale transistors.

A Unified Scalable Quasi-Ballistic Transport Model of GFET for Circuit Simulations

A unified quasi-ballistic transport model is developed for single- and double-gate graphene field-effect transistors (GFETs) using the McKelvey flux theory approach. The proposed model is compact, scalable, and compatible for the simulation of I-V characteristics of GFET for all regions of device operation. The drain current equation (IDS) incorporates the formulation of quasithermal velocity, quasi-ballistic mobility of charge carrier (describe the carrier transport of 2-D material like graphene), and source/drain backscattering coefficient. This model is also capable to describe the mobility of graphene material in degenerate and nondegenerate states. The GFET with different channel lengths, widths, and oxide thicknesses is simulated using this model for single- and double-gate devices. The proposed model synchronized with experimental results and explains the peculiar transport characteristics of GFET with normalized root-mean-square error less than 9%.

Quasi-ballistic transport model for top- and back-gated graphene nanoribbon field-effect transistors

A carrier transport model for graphene nanoribbon field-effect transistors (GNR FETs) is obtained using McKelvey’s flux and quasi-ballistic transport theories. Source/drain series resistances are taken into account. With the model, an analytical expression for drain-to-source current is achieved including only three fitting parameters. The model is verified by simulation, and good agreements are observed. With the model, the drain-to-source current characteristics of GNR FETs with different drain or gate biases can be obtained very swiftly, saving much simulation time. The model will provide some design insights into the practical use of GNR FETs.

Modeling of quasi-ballistic transport in nanowire metal-oxide-semiconductor field-effect transistors

We developed a semi-analytical quasi-ballistic transport model for the nanowire metal-oxide-semiconductor field-effect transistors, dealing with finite lengths of source, channel, and drain. For the modeling, we used a combination of one-flux scattering matrices and analytical solutions of Boltzmann transport equations. The developed model was in quantitatively good agreement with numerical results, and well represented intermediate-scaled devices. In addition, we illustrated that the finite source seriously affect the distribution function of the carriers injected from the source, and the finite drain does for the backscattering into the channel from the drain. Finally, our model and results would help to understand physical aspects regarding quasi-ballistic transport in nanoscale devices.

Effects of Roughness Scattering in Carrier Transport of Near Ballistic Silicon NanoWire MOSFET

– In this paper, we have investigated the Scattering effects in Carrier Transport of Near-ballistic SiNW MOSFET, which incorporates elastic scattering, optical phonon emission and its combination with Roughness Scattering. Current–voltage (I–V) characteristics of Proposed model is compared with Natori’s Ballistic and Quasi-Ballistic Transport model. We study the impact of Surface Roughness in the device leads on the current variability of a Gate-All-Around (GAA) SiNW MOSFET, which shows a remarkable decrease in electric current, mobility variation and transconductance because of scattered mobility. Analog parameters like the transconductance (gm), the transconductance generation factor (gm/Id), the early voltage (VA) have also been investigated. Effectiveness of the proposed model has been confirmed by comparing the analytical results with the TCAD simulation results.

Quasi-Ballistic Transport Model for Graphene Field-Effect Transistor

Based on McKelvey's flux theory, a carrier transport model for a graphene field-effect transistor (GFET) is addressed. This model leads to an explicit expression for drain-to-source current with only a few fitting parameters. The model is verified with experiments and simulations, and good agreements are observed. With the model, the characteristics of drain-to-source current of the GFET with positive or negative gate biases can be obtained very quickly and easily. The model will provide some insights and guidance for the practical use of the GFETs and can be embedded in circuit simulation tools.