A model of carrier density and drain current for monolayer graphene field-effect transistors

Abstract

A model of carrier density and drain current for monolayer graphene field-effect transistors (GFET) is proposed in this paper. In general, the carrier density is the numerical integration of the density of states (DOS) and Fermi-Dirac distribution. To avoid numerical solution, a physical-based and analytical calculation for carrier density and quantum capacitance is presented. Due to the intrinsic physical mechanism, the interface trap density is taken into account in the drain current model of GFET. Through the comparisons between model results and numerical iterations or experimental data, the validity of the proposed models is supported. The clear physical conception and simplicity of algorithm make our scheme suitable for compact modelling.

A numerical model of electrical characteristics for the monolayer graphene field effect transistors

“…The equivalent capacitive circuit of the top-gate GFET is depicted in Figure 2. The channel potential V(x) is zero at x = 0 and equals to the drain-source voltage V DS at x = L. The dependency of C q on voltage drop V ch in graphene can be evaluated by introducing a capacitance weighting factor 0.5 [11,19], thus we get the overall net mobile charge density:…”

“…Then the carrier velocity y is obtained by substituting equation (13) and equation (17) into equation (9). Eventually, the current I ds can be calculated using equation (1), which can be rewritten as [11,19]:…”

“…Many researchers investigated the drain-source current model of MLG based on the linear dispersion and provided proper reproduction of current-voltage characteristics for experimentally fabricated graphene field effect transistors (GFETs) [5,6], but with the carrier saturation velocity (y sat ) significantly overestimated when the carrier density is small. Meanwhile, the inevitablely presented impurities lead to the formation of inhomogeneous electron-hole puddles [7][8][9], therefore the linear Dirac carrier dispersion breaks up into a disordered graphene system in MLG [10][11][12][13][14][15]. The effects of disorder on the quantum capacitance and carrier density of graphene devices have been studied for the first time using a Gaussian distribution of the potential fluctuations [13][14][15].…”

“…The effects of disorder on the quantum capacitance and carrier density of graphene devices have been studied for the first time using a Gaussian distribution of the potential fluctuations [13][14][15]. The exponential distribution model is an approximation of the physics-based Gaussian model which leads to analytical expression for quantum capacitance and drain-source current [10][11][12]. It is illustrated that the potential fluctuation function of the exponential distribution is valid in disordered systems.…”

“…The material disorder affects the density of states (DOS) distribution in GFETs, and therefore affects r and y sat . It's worth noting that the effect of disorder on y sat at low channel carrier density is usually based on the fitting of the relevant parameters [11,18], which lacks specific physical meaning.…”