Effect of chiral property on hot phonon distribution and energy loss rate due to surface polar phonons in a bilayer graphene

Abstract

Effect of chiral property on hot phonon distribution and hot electron energy loss rate due to surface polar phonons is investigated in a supported bilayer graphene. Hot phonon distribution Nq(ω0) with chiral property shows a new feature of appearance of a cusp. Interestingly, minimum of the cusp is shifting toward larger q and its width is increasing as electron concentration ns increases. The maximum value of Nq(ω0) is found to shift toward lower q with the increasing ns. This unusual behavior is not found in conventional two-dimensional electron gas (2DEG). The effect of chiral property on energy loss rate is found to be less significant. Hot phonon effect on energy loss rate is studied as a function of electron temperature and electron concentration for different substrates. It is found to reduce the energy loss rate significantly and the results are compared with those in conventional 2DEG. We believe that the magnitude of hot phonon effect depends both on dielectric constant of the substrate and surface polar phonon energy.

Hot carrier relaxation of Dirac fermions in bilayer epitaxial graphene

“…in theoretical studies [11][12][13] and falls in the relatively broad range (10-50 eV) found in the literature [33][34][35][36].…”

“…So far, no theoretical extension of the "supercollisions" to bilayer graphene has been reported and our results show no evidence of the transition to a T 3 dependence as observed in monolayer graphene. Another possible cooling mechanism to retain the energy loss rate increasing as T 4 in a substrate supported bilayer graphene sample could be the interaction between hot electrons and surface polar phonons (SPPs) [11][12][13], combined with hot phonon effects which occur when the hot phonon decay rate is not as fast as the phonon emission rate. However, theoretical calculations based on a SiC substrate suggest the contribution from SPPs can only be clearly observed for electron temperatures higher than 100 K [13], due to the relatively low dielectric constant and high surface polar phonon energies of SiC, compared with substrates such as HfO 2 .…”

“…Energy loss rates, together with electron-phonon relaxation times are extracted in the carrier temperature range of 1.4 K to around 100 K and the carrier density dependence is determined. We then make comparisons between our data and theoretical predictions [11][12][13], as well as the energy loss behaviour in monolayer graphene [6,7,14].…”

“…Very recently, energy loss rates for hot carriers in bilayer graphene have been theoretically explored taking into account the interactions of electrons with acoustic and surface polar phonons as well as hot phonon effects [11][12][13], but to date this has yet to be studied in significant detail experimentally.…”

Hot-electron cooling by acoustic and optical phonons in monolayers ofMoS2and other transition-metal dichalcogenides

“…This is similar to findings in GaAs QWs 69,71 and in bilayer graphene. 68 In the q range where the elph scattering rate in Fig. 9 exceeds τ −1 ph , the effective temperature of the hot phonons approaches a value T eff ∼ T e close to the hot-electron temperature which leads to the reduction of the cooling power due to optical phonons shown in Figs.…”