Mobility in semiconducting graphene nanoribbons: Phonon, impurity, and edge roughness scattering

The transport properties of carriers in semiconducting graphene nanoribbons are studied by comparing the effects of phonon, impurity, and line-edge roughness scattering. It is found that scattering from impurities located at the surface of nanoribbons and from acoustic phonons are as important as line-edge roughness scattering. The relative importance of these scattering mechanisms varies with the temperature, Fermi-level location, and the width of the ribbons. Based on the analysis, strategies for improvement of low-field mobility are described.

Figure 1

Schematic representation of LER scattering in GNRs. The variation in the GNR width leads to spatial variation in the band gap, and the fluctuations in the band edges cause carrier scattering and reduction in mobility.

Figure 2

(Color online) Line-edge roughness scattering rates in GNRs (a) for various GNR widths $W$ plotted against a range of roughness amplitudes ($H$ normalized to the widths $W$) and (b) for a 5-nm-wide ribbon for various Fermi levels plotted against various roughness correlation lengths $\Lambda$.

Figure 3

Schematic representation of the GNR and charged impurities that cause scattering of mobile carriers.

Figure 4

(Color online) Scattering rates due to various scattering mechanisms for a 5-nm-wide GNR as a function of the carrier energy.

Figure 5

(Color online) Carrier mobility in a 5 nm GNR as a function of temperature for three distinct Fermi levels. The relative importance of the various scattering rates can be ascertained from the plots. $E_c$ is the energy difference between the conduction-band edge and the Dirac point of the underlying graphene band structure.

Figure 6

(Color online) Carrier mobility in a 3 nm GNR as a function of temperature for three distinct Fermi levels.

Figure 7

For very narrow ribbons, LER scattering is seen to be the mobility-limiting scattering mechanism but wider GNRs—even for widths greater than $\sim 5\text{nm}$ are relatively insensitive to LER scattering. For such ribbons, the mobility at room temperature is limited by acoustic-phonon scattering.