Search

We have studied, in bilayer graphene (BLG), the hot electron cooling power F VP ( T , n s ) due to acoustic phonons via vector potential (VP) coupling. It is calculated as a function of electron concentration n s and temperature T and compared with F DP ( T , n s ), the contribution from the deformation potential (DP) coupling. For the n s around 1 × 10 12 cm −2 , F VP ( T , n s ) is much smaller than F DP ( T , n s ). With increase of n s , F DP ( T , n s ) decreases faster than F VP ( T , n s ) does. A cross over is predicted and dominant contribution of F VP ( T , n s ) can be observed at large n s . In the Bloch- Grüneisen (BG) regime F VP ( T , n s ) ~ n s −1/2 and F DP ( T , n s ) ~ n s −3/2 . Both F VP ( T , n s ) and F DP ( T , n s ) have the same T dependence with T 4 power law in the BG regime. Behaviour of F DP ( T , n s ) ~ n s −3/2 and T 4 is in agreement with the experimental results at moderate n s . Besides, in the BG regime, we have predicted, for both the VP and DP coupling, a relation between F ( T , n s ) and the acoustic phonon limited mobility μ p , opening a new door to determine μ p from the measurements of F ( T , n s ) [ABSTRACT FROM AUTHOR]

Abstract: The high electric field transport properties namely, hot electron energy loss rate P, momentum loss rate Q, electron temperature T e and drift velocity V d 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 T e 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 ~T e 4 (T e 2.5), with a new feature of a kink appearing due to the chiral nature of the electrons. The predicted T e 4 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 T e>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. T e and V d 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). T e is found to increase with the increasing electric field and is significantly enhanced by the hot phonon effect. Low field V d 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 V d. The presence of disorders CI and SD reduces V d significantly and in clean samples larger saturation velocity can be achieved at a relatively smaller E. [Copyright &y& Elsevier]

Abstract: Electronic thermal conductivity κ e is investigated, using Boltzmann transport equation approach, in a suspended and supported bilayer graphene (BLG) as a function of temperature and electron concentration. The electron scattering due to screened charged impurity, short-range disorder and acoustic phonon via deformation potential are considered for both suspended and supported BLG. Additionally, scattering due to surface polar phonons, is considered in supported BLG. In suspended BLG, calculated κ e is compared with the experimental data leaving the phonon thermal conductivity. It is emphasized that κ e is important in samples with very high electron concentration and reduced phonon thermal conductivity. κ e is found to be about two times smaller in supported BLG compared to that in suspended BLG. With the reduced extrinsic disorders, in principle, the intrinsic scattering by acoustic phonons can set a fundamental limit on possible intrinsic κ e. [Copyright &y& Elsevier]

Abstract: We calculate the hot electron energy relaxation P due to acoustic–phonon scattering via deformation potential coupling in an armchair graphene nanoribbon (AGNR). Its dependence on electron temperature T e , Fermi energy E f (linear electron concentration n l ) and width W of AGNR is investigated. At low T e , P is found to be exponentially suppressed contrary to the power laws in graphene and conventional semiconductor nanostructures. This gradually changes to sublinear behavior for an about T e >100K contrary to conventional P∼T e . P shows strong dependence on E f and n l and it decreases with the increasing E f and n l at low T e . At a constant n l , P varies approximately as W −s with s∼2–3. A weak dependence of s on T e and n l is observed. We point out that the low T e study of P, as it is independent of all non-acoustic phonon scattering mechanisms, could be used to determine the accurate value of acoustic–phonon deformation potential coupling constant in graphene about which there is still uncertainty. [Copyright &y& Elsevier]