Transport properties of 2D graphene containing structural defects

We propose an extensive report on the simulation of electronic transport in 2D graphene in presence of structural defects. Amongst the large variety of such defects in sp$^2$ carbon-based materials, we focus on the Stone-Wales defect and on two divacancy-type reconstructed defects. First, based on ab initio calculations, a tight-binding model is derived to describe the electronic structure of these defects. Then, semiclassical transport properties including the elastic mean free paths, mobilities and conductivities are computed using an order-N real-space Kubo-Greenwood method. A plateau of minimum conductivity ($\sigma^{min}_{sc}= 4e^2/\pi h$) is progressively observed as the density of defects increases. This saturation of the decay of conductivity to $\sigma^{min}_{sc}$ is associated with defect-dependent resonant energies. Finally, localization phenomena are captured beyond the semiclassical regime. An Anderson transition is predicted with localization lengths of the order of tens of nanometers for defect densities around 1%.Comment: 17 pages, 17 figures, submitted to Phys. Rev.

Carrier transport of rough-edged doped GNRFETs with metal contacts at various channel widths

Graphene nanoribbons (GNRs) have attracted much attention owing to their exotic electronic properties. However, it is impossible to fabricate GNRs with perfect edges. The edge roughness effect will degrade the performance of the field effect transistor (FET). Therefore, modelling GNR FETs (GNRFETs) with the line-edge roughness effect and doping is crucial for evaluating the performance metrics of these devices. In this research study, the carrier transport properties of double-gate, monolayer, doped, rough-edged armchair GNRFETs (AGNRFETs) with various channel widths, and metallic zigzag GNR (ZGNR) contacts are studied. The investigated width index originates from the 3p+1 family, and step and edge doping with nitrogen atoms (n-doping) and boron atoms (p-doping) are applied. In addition, the nearest-neighbour tight-binding method is employed to build the Hamiltonian matrix of the device. The self-consistent solutions of the Poisson and Schrödinger equations are computed with the recursive non-equilibrium Green's function (NEGF) method and successive over-relaxation (SOR) method to minimise the time consumption for convergence. The carrier transport properties of the pristine and non-pristine devices (e.g. the total density of states (DOS), transmission coefficient, energy-resolved current spectrum, and various current–voltage characteristics) are simulated. Based on the output, the performance metrics of the device, including the subthreshold swing, drain-induced barrier lowering (DIBL), threshold voltage, and on/off current ratio, are calculated. The results of different widths are compared separately and for the pristine and doped rough-edged channel devices. For narrower devices, the subthreshold swing and DIBL decrease, whereas the threshold voltage and on/off current ratio increase. The subthreshold swing and DIBL of the doped rough-edged channel device are superior to those of the pristine channel device. Moreover, the on-current, threshold voltage, and on/off current ratio of the rough-edged channel improve with dopants. N-doping achieves a much higher current in the on-state owing to the lighter electron mass and faster electron velocity compared with those of holes. Furthermore, the n-type rough-edged seven-armchair GNRFET with a length of 5 nm exhibits an outstanding subthreshold swing of approximately 85.2 mV/dec and a DIBL of 63.03 mV/V. Thereby, the narrower doped, rough-edged device is less affected by short-channel effects and exhibits lower leakage currents in the off-state. This results in a better switching performance, which makes it a potential candidate for future nano-electronic applications with low-power design