Design of GNRFET using different doping profiles near the source and drain contacts

The graphene nanoribbon field effect transistors (GNRFET) suffer from band-to-band tunnelling (BTBT), which in turn causes ambipolar conduction. In this simulation study, we propose a step-linear doping profile for the graphene nanoribbon near the source and drain contacts. This type of doping profile suppresses the BTBT and ambipolar conduction of the transistor. The proposed step-linear dopant distribution efficiently modulates the potential barrier at the source-channel interface, increases the width of the tunnelling region, and thus reduces the OFF-state current by decreasing the possibility of BTBT. A p(z) orbital band model with the nearest neighbour is used to simulate the graphene nanoribbon. The Schrodinger equation is solved by non-equilibrium Green's function method to achieve the charge density. In order to calculate the electrostatic potential, the Poisson's equation is solved by means of the non-linear finite difference method. We have used the uncoupled mode space approach significantly to reduce the computational time. It is shown that the proposed doping profile improves the performance of graphene nanoribbon transistor by decreasing the OFF-state current and increasing the ON-state current. We have also observed a slight improvement in the subthreshold slope of the proposed GNRFET. The proposed GNRFET is more suitable than the conventional GNRFETs for switching applications.