Gated Graphene Nanoribbons Research Articles

A gate-induced switch in zigzag graphene nanoribbons and charging effects

Using the non-equilibrium Green’s function formalism, we investigate nonlinear transport andcharging effects of gated graphene nanoribbons (GNRs) with an even number of zigzag chains.We find a negative differential resistance (NDR) over a wide range of gate voltages with anon/off ratio ∼ 106 for narrow enough ribbons. This NDR originates from the parity selection rule and alsoprohibition of transport between discontinuous energy bands. Since the external field is wellscreened close to the contacts, the NDR is robust against the electrostatic potential.However, for voltages higher than the NDR threshold, due to charge transfer through theedges of the zigzag GNR (ZGNR), screening is reduced such that the external potential canpenetrate inside the ribbon giving rise to smaller values of off-current. Furthermore, theon/off ratioof the current depends on the aspect ratio of the length/width and also edge impurity. Moreover, theon/off ratio displays a power law behavior as a function of ribbon length.

Perfect Reflection of Chiral Fermions in Gated Graphene Nanoribbons

Perfect Reflection of Chiral Fermions in Gated Graphene Nanoribbons

Uniaxial Strain Effects on the Performance of a Ballistic Top Gate Graphene Nanoribbon on Insulator Transistor

The effects of uniaxial strain on the bandgap and performance of a top gate graphene nanoribbon (GNR) on insulator transistor are studied using pi-orbital basis 3-D ballistic quantum simulation. The bandgap variation with strain shows zigzag pattern for the three families of nanoribbon. The variation is linear between two turning points and has almost equal magnitude of gradient for all the families. The ON-state and the off-state currents reduce and the ON/OFF current ratio increases with the type of strain that results in larger bandgap. The variation of off current and ON/OFF current ratio is exponential, and that of on current is linear with strain and is independent of the type of strain applied. The intrinsic switching delay reduces and the intrinsic cutoff frequency increases with the type of strain that results in smaller bandgap. While the off -state current and the on/off current ratio improve with strain, the on-state current and switching performance degrade, and vice versa. Therefore, careful tradeoff should be considered in strain engineering of GNR transistors.

Perfect Reflection of Chiral Fermions in Gated Graphene Nanoribbons

We describe the results of a theoretical study of transport through gated metallic graphene nanoribbons using a nonequilibrium Green function method. Although analogies with quantum field theory predict perfect transmission of chiral fermions through gated regions in one dimension, we find perfect reflection of chiral fermions in armchair ribbons for specific configurations of the gate. This effect should be measurable in narrow graphene constrictions gated by a charged carbon nanotube.

Transport and performance of a zero-Schottky barrier and doped contacts graphene nanoribbon transistors

The transport physics and performance of a top gate graphene nanoribbon (GNR) on an insulator transistor are studied for both the MOSFET like doped source–drain and the zero-Schottky barrier source–drain contacts. A voltage controlled tunnel barrier is the device transport physics. The doped source–drain contact device has a higher gate capacitance, higher transconductance, higher on/off current ratio and higher on-state current. The higher on-state current results in a lower switching delay of 17 fs, and the higher transconductance results in a higher intrinsic cut-off frequency of 27 THz in the doped source–drain contact device. The gate voltage, beyond the source–channel flat band condition, modulates both the tunnel and the thermal barrier in the doped source–drain contact devices and the tunnel barrier only in the Schottky contact devices. This limits the on-state current of Schottky contact devices.