Scattering mechanisms and diffusion thermopower in a bilayer graphene

• Acoustic phonon limited mobility shows temperature dependence of T−4, a signature of 2D phonons.
• Sd linear up to 100 K.
• Sd∼ns−1, ns is the carrier concentration.

Diffusion thermopower Sd is studied along with the scattering mechanisms and mobility μ by the Boltzmann transport equation technique in a bilayer graphene (BLG). Particular emphasis is made with respect to the sensitivity of Sd and μ to the possible scattering due to acoustic phonons (ap) and surface polar phonons (spp), charged impurity (ci) and short range disorder (sd). In the Bloch–Gruneisen regime, μap due to acoustic phonons shows T−4 behavior, a characteristic of 2D phonons, but with a small bump attributing to the chiral property of electrons. μ due to ci and sd are found to be almost independent of T. Numerical results of Sd, due to each of these mechanisms and the resultant, are presented as a function of temperature T and electron concentration ns for both supported and suspended BLG. The resultant Sd and that due to ap, ci and sd are found to be ∼T up to 100 K and vary sublinearly above this temperature. However, the range of linear T behavior will be larger for larger ns.Sd due to sd is found to be dominant. A qualitative agreement is found with the experimental data. Sd∼ns−1 over the range of interest considered. Sd in suspended BLG is found to be greater than that in the supported one.

Diffusion thermopower Sd is shown as a function of temperature due to different scattering mechanisms.Figure optionsDownload as PowerPoint slide