High field transport properties of a bilayer graphene

Abstract

The high electric field transport properties namely, hot electron energy loss rate P, momentum loss rate Q, electron temperature Te and drift velocity Vd are studied theoretically in a bilayer graphene (BLG) by employing the momentum and energy balance technique. P and Q are investigated as a function of Te by considering the electron interaction with the acoustic phonons (APs) and the surface polar phonons (SPPs). In the Bloch–Grüneisen regime P (Q) due to APs is ~Te4 (Te2.5), with a new feature of a kink appearing due to the chiral nature of the electrons. The predicted Te4 is consistent with the recent experimental observation of heat resistance (Yan et al. Nature Nanotechnology 3 (2012) 472 [35]). Hot phonon effect is taken into account for SPPs. A dip has been observed in the hot phonon distribution of SPPs, a new feature, which is not found in conventional two-dimensional electron gas, and this can be attributed to the chiral nature of the electrons. P (Q) due to SPPs is found to be dominant at about Te>150 (180)K for a lattice temperature T=4.2K. It is observed that the hot phonon effect is found to reduce P and Q due to SPPs significantly. Te and Vd are calculated as a function of the electric field E by taking into account the additional channels for momentum relaxation due to Coulomb impurity (CI) and short-range disorder (SD). Te is found to increase with the increasing electric field and is significantly enhanced by the hot phonon effect. Low field Vd is found to be limited by CI, SD and APs and in the high field region it reaches a near saturation value. The hot phonon effect tends to reduce the value of Vd. The presence of disorders CI and SD reduces Vd significantly and in clean samples larger saturation velocity can be achieved at a relatively smaller E.