Intrinsic electron-and hole-phonon interactions are investigated in monolayer transition metal dichalcogenides MX 2 (M=Mo,W; X=S,Se) based on a density functional theory formalism. Due to their structural similarities, all four materials exhibit qualitatively comparable scattering characteristics with the acoustic phonons playing a dominant role near the conduction and valence band extrema at the K point. However, substantial differences are observed quantitatively leading to disparate results in the transport properties. Of the considered, WS 2 provides the best performance for both electrons and holes with high mobilities and saturation velocities in the full-band Monte Carlo analysis of the Boltzmann transport equation. It is also found that monolayer MX 2 crystals with an exception of MoSe 2 generally show hole mobilities comparable to or even larger than the value for bulk silicon at room temperature, suggesting a potential opportunity in p-type devices. The analysis is extended to estimate the effective deformation potential constants for a simplified treatment as well.

The electron-phonon interaction and related transport properties are investigated in monolayer silicene and MoS 2 by using a density functional theory calculation combined with a full-band Monte Carlo analysis. In the case of silicene, the results illustrate that the out-of-plane acoustic phonon mode may play the dominant role unlike its close relative, graphene. The small energy of this phonon mode, originating from the weak sp 2 π bonding between Si atoms, contributes to the high scattering rate and significant degradation in electron transport. In MoS 2 , the longitudinal acoustic phonons show the strongest interaction with electrons. The key factor in this material appears to be the Q valleys located between the and K points in the first Brillouin zone as they introduce additional intervalley scattering. The analysis also reveals the potential impact of extrinsic screening by other carriers and/or adjacent materials. Finally, the effective deformation potential constants are extracted for all relevant intrinsic electron-phonon scattering processes in both materials.

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...

Density functional perturbation theory is used to analyze electron-phonon interaction in bilayer graphene. The results show that phonon scattering in bilayer graphene bears more resemblance with bulk graphite than monolayer graphene. In particular, electron-phonon scattering in the lowest conduction band is dominated by six lowest (acoustic and acoustic-like) phonon branches with only minor contributions from optical modes. The total scattering rate at low/moderate electron energies can be described by a simple two-phonon model in the deformation potential approximation with effective constants D ac ≈ 15 eV and D op ≈ 2.8 × 10 8 eV/cm for acoustic and optical phonons, respectively. With much enhanced acoustic phonon scattering, the low field mobility of bilayer graphene is expected to be significantly smaller than that of monolayer graphene.

The intrinsic carrier transport dynamics in phosphorene is theoretically examined.Utilizing a density functional theory treatment, the low-field mobility and the saturation velocity are characterized for both electrons and holes in the monolayer and bilayer structures. The analysis clearly elucidates the crystal orientation dependence manifested through the anisotropic band structure and the carrier-phonon scattering rates. In the monolayer, the hole mobility in the armchair direction is estimated to be approximately five times larger than in the zigzag direction at room temperature (460 cm 2 /Vs vs. 90 cm 2 /Vs). The bilayer transport, on the other hand, exhibits a more modest anisotropy with substantially higher mobilities (1610 cm 2 /Vs and 760 cm 2 /Vs, respectively). The calculations on the conduction-band electrons indicate a comparable dependence while the characteristic values are generally smaller by about a factor of two. The variation in the saturation velocity is found to be less pronounced.With the anticipated superior performance and the diminished anisotropy, few-layer phosphorene offers a promising opportunity particularly in p-type applications.