Negative differential resistance effect in different structures of armchair graphene nanoribbon

Graphene is a one-atom-thick stable covalently bonded carbon layer ordered in a honeycomb lattice. Single layer graphene of nanoscale width (including a few numbers of atoms across the width) is known as Graphene Nanoribbon, GNR. Armchair chirality of GNR provides appropriate value of band gap (in the range of that of common semiconductors), whereas its bandgap is tunable by only changing the width of ribbon. These two properties in addition to availability in two-dimension and very high carrier mobility made GNR a unique semiconductor substance in recent years. Therefore, in the past few years it has gained lots of attention for its interesting properties and applications such as: sensors, filters, detectors and switches. On the other hand, passivation of edges of GNR plays a fantastic role in its electrical behavior, where by implementing some special configuration for passivation Negative-Differential-Resistance (NDR) can be created. Graphene-based NDR behavior creates a great potential for providing some new devices in electronics. This work is focused on armchair graphene nanoribbons (AGNR) for its semiconducting behavior, where the edges of ribbon have significant effects on the current-voltage characteristic of the device. We report a theoretical investigation and numerical simulation of the effect of passivating the edges on the carrier transport in AGNRs. The number of carbon atoms across the ribbon width is an important parameter that we selected ten atoms to have a suitable size for simulation and appropriate band gap energy as a semiconductor material. Calculations are done based on density functional theory (DFT) and using Green's function of atomic structure of the device. Four types of edge terminations as: H-edged-AGNR, O-edged-AGNR, homo H-O-edged-AGNR and hetero H-O-edged-AGNR terminations are investigated in detail. It is shown that the edge termination of graphene nanoribbons by a special arrangement of both hydrogen and oxygen atoms causes NDR behavior which can have interesting applications in nanoelectronics and nanosensors. In addition, the oxygen atoms edge termination demonstrates NDR behavior, while such a behavior is not observed by only hydrogen atoms edge termination.