The electron-phonon interaction in monolayer graphene is investigated using density-functional perturbation theory. The results indicate that the electron-phonon interaction strength is of comparable magnitude for all four in-plane phonon branches and must be considered simultaneously. Moreover, the calculated scattering rates suggest an acoustic-phonon contribution that is much weaker than previously thought, revealing an important role of optical phonons even at low energies. Accordingly it is predicted, in good agreement with a recent measurement, that the intrinsic mobility of graphene may be more than an order of magnitude larger than the already high values reported in suspended samples. DOI: 10.1103/PhysRevB.81.121412 PACS number͑s͒: 72.10.Di, 71.15.Mb, 72.80.Vp Graphene, a two-dimensional ͑2D͒ sheet of carbon atoms in a honeycomb lattice, continues to attract much attention due to its unique physical properties. Aside from a substantial academic interest resulting from the relativisticlike behavior of charge carriers, this material is considered very promising in device applications as it has an extremely high intrinsic mobility, even at room temperature. Although in realistic conditions ͑i.e., placed on a substrate͒ the mobility tends to decrease significantly due to the presence of additional scattering mechanisms at the interfaces, 1-3 much effort is currently being devoted to eliminate, or at least minimize, these effects which are detrimental to graphene transport characteristics. Therefore, it is crucial to develop an accurate knowledge of the electron-phonon scattering as it determines the ultimate limit of any electronic device performance. The strength of electron-phonon coupling is typically estimated using the deformation potential approximation ͑DPA͒; it has been applied for graphene by a number of authors. [4][5][6] When the corresponding deformation potential constant was estimated from the transport measurements, however, the results revealed a discrepancy that is too large to be ignored. 1,2,7 Moreover, a very recent observation of mobilities in excess of 10 7 cm 2 / V s at T Շ 50 K in the decoupled graphene 8 drastically departs from the conventionally accepted values, raising serious questions about the current understanding of the intrinsic transport characteristics of graphene. A detailed theoretical analysis of electron-phonon interaction beyond the DPA is clearly called for. In this work, we apply a first-principles approach based on density-functional theory ͑DFT͒ to calculate the electronphonon coupling strength in graphene. The obtained electron-scattering rates associated with all phonon modes are analyzed and the intrinsic resistivity and mobility of monolayer graphene are estimated as functions of temperature. The results clearly elucidate the role of different branches ͑particularly, the significance of optical phonons and intervalley scattering via acoustic phonons͒ as well as limitations of DPA. The obtained effective deformation potential constants suggest the possibil...

Effect of chiral property on hot phonon distribution and energy loss rate due to surface polar phonons in a bilayer graphene J. Appl. Phys. 113, 063705 (2013); 10.1063/1.4790309Phonon-limited electron mobility in graphene calculated using tight-binding Bloch waves J. Appl. Phys. 112, 053702 (2012); 10.1063/1.4747930 Two-dimensional electron gases: Theory of ultrafast dynamics of electron-phonon interactions in graphene, surfaces, and quantum wellsThe effects of surface polar phonons on the electronic transport properties of monolayer graphene are studied by using a Monte Carlo simulation. Specifically, the low-field electron mobility and saturation velocity are examined for different substrates ͑SiC, SiO 2 , and HfO 2 ͒ in comparison to the intrinsic case. While the results show that the low-field mobility can be substantially reduced by the introduction of surface polar phonon scattering, corresponding degradation of the saturation velocity is not observed for all three substrates at room temperature. It is also found that surface polar phonons can influence graphene's electrical resistivity even at low temperature, leading potentially to inaccurate estimation of the acoustic phonon deformation potential constant.

The influence of electron-electron scattering on the distribution function and transport characteristics of intrinsic monolayer graphene is investigated via an ensemble Monte Carlo simulation. Due to the linear dispersion relation in the vicinity of the Dirac points, it is found that pair-wise collisions in graphene do not conserve the ensemble average velocity in contrast to conventional semiconductors with parabolic energy bands. Numerical results indicate that electron-electron scattering can lead to a decrease in the low field mobility by more than 80 % for moderate electron densities. At high densities, the impact gradually diminishes due to increased degeneracy.Since graphene was first realized experimentally in 2004, 1 it has attracted significant interest due to its unique electronic properties. At low electron energies near the inequivalent Dirac points, there is no gap between the valence and conduction bands and the dispersion of the energy bands is linear. 2 Extremely high electrical mobilities have been reported in suspended graphene, exceeding 10 5 cm 2 /Vs near room temperature, 3 suggesting potential applications to ultrahigh frequency electronic devices. 4 The carrier density, which is controlled by the gate voltage, can be expected to vary by orders of magnitude. An interesting consequence of the linear energy dispersion is that the ensemble average velocity is not necessarily conserved upon an electronelectron (e-e) scattering event. Accordingly, inter-carrier collisions deserve careful consideration in the determination of the transport properties.Das Sarma et al. 5 found the inelastic e-e scattering rate and mean free path in graphene through the analysis of the quasiparticle self-energies. The scattering rate, calculated for electron densities from 1−10×10 12 cm −2 , was found to be of the same order of magnitude for electronphonon scattering rates evaluated in the deformation potential approximation (DPA). 6 Several authors have considered the electronic transport properties of graphene based on approaches such as the Monte Carlo simulation (see, for example, Ref. 7); however, the effects of e-e scattering have yet to be addressed to the best of our knowledge. In the present study, we examine the influence of this interaction mechanism in intrinsic monolayer graphene at room temperature. A full-band ensemble Monte Carlo method is used for accurate analysis of the distribution function as well as its macroscopic manifestations, particularly, the electron low-field mobilities and drift velocities.In both bulk and two-dimensional (2D) conventional semiconducting systems, e-e scattering has been well studied as is documented in the literature. 8 During an e-e scattering event, both the energy and momentum are conserved. In a parabolic band structure, common in conventional semiconductors, momentum conservation directly leads to the conservation of velocity. This can be readily shown by multiplying the momentum conservation equation by /m, which givesIt is then clear that, in a material with a p...

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By the use of the Monte Carlo method, we studied the distribution function and the basic characteristics of hot electrons in InN, GaN, and AlN under moderate electric fields. We found that in relatively low fields (of the order of kV/cm) the optical phonon emission dominates in the electron kinetics. This strongly inelastic process gives rise to a spindle-shaped distribution function and an extended portion of a quasisaturation of the current–voltage (I–V) characteristics (the streaming-like regime). Formation of this regime is induced by a suppression of the electron spreading over the momenta perpendicular to the electric field. We prove that this is a universal character of the hot electron behavior for all three nitrides. The effects can be detected by the measurement of the I–V characteristics, or the thermopower of hot electrons in the transverse direction.