Ab initioelectron mobility and polar phonon scattering in GaAs

Abstract

In polar semiconductors and oxides, the long-range nature of the electron-phonon (e-ph) interaction is a bottleneck to compute charge transport from first principles. Here, we develop an efficient ab initio scheme to compute and converge the e-ph relaxation times (RTs) and electron mobility in polar materials. We apply our approach to GaAs, where by using the Boltzmann equation with state-dependent RTs, we compute mobilities in excellent agreement with experiment at 250-500 K. The e-ph RTs and the phonon contributions to intravalley and intervalley e-ph scattering are also analyzed. Our work enables efficient ab initio computations of transport and carrier dynamics in polar materials. DOI: 10.1103/PhysRevB.94.201201 Semiconductors with polar bonds, such as III-V and II-VI compounds, and oxides, are important in condensed matter physics and for technological applications. Charge transport in these polar materials plays a key role in electronics, optoelectronic, photovoltaics, and photocatalysis. Novel experiments [1,2] are dramatically advancing the understanding of charge transport in polar materials. Yet, their microscopic interpretation requires detailed knowledge of the carrier scattering processes. Since fabricating pure crystals is challenging for many polar materials, extracting intrinsic charge transport properties from experiment is nontrivial; questions related to the role of doping, impurities, and defects often arise when interpreting transport measurements.Ab initio computational approaches to study the carrier transport and scattering mechanisms are uniquely poised to advance the understanding of polar materials. Ab initio calculations of carrier mobility [3][4][5][6][7][8][9] and scattering [10][11][12][13] are a recent development, and have been reported so far only for a few metals and nonpolar semiconductors. However, the mobility in polar semiconductors and oxides, which is the focus of this Rapid Communication, is still typically investigated with semiempirical models [1,14]. One major challenge in computing transport in polar materials is the Fröhlich interaction [15], a long-range coupling between electrons and longitudinal optical (LO) phonons. Electronphonon (e-ph) scattering due to LO modes, and in general to polar phonons (PPs), is typically the main carrier scattering mechanism in polar materials, but it cannot yet be included in ab initio transport calculations.When computed directly using density functional perturbation theory (DFPT) [16], the e-ph matrix elements correctly include the Fröhlich interaction for arbitrary values of the phonon wave vector q. Yet, the very large number of e-ph matrix elements necessary to converge the mobility and the e-ph relaxation times (RTs) [10-12] make direct DFPT calculations impractical due to computational cost. For metals and nonpolar semiconductors, in which the e-ph interaction is short ranged, Wannier interpolation [17] can be employed to obtain e-ph matrix elements on fine Brillouin zone (BZ) grids. In polar materials, Wannier interpolati...

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

“…The scheme developed in our recent work [32] is applied to converge e-ph nk . The relaxation times τ nk used in the mobility calculations are the inverse of the scattering rates, τ nk = 1/ e-ph nk .…”

“…Methods combining band theory and many-body perturbation theory have been recently employed to accurately compute electron-phonon (e-ph) scattering and charge transport, for now in simple inorganic materials with a handful of atoms in the unit cell [31][32][33][34]. Due to computational cost, these calculations have not yet been applied to organic crystals with tens of atoms in the unit cell.…”

“…Due to computational cost, these calculations have not yet been applied to organic crystals with tens of atoms in the unit cell. Ab initio studies of e-ph coupling in organic crystals exist [35][36][37], but charge transport, which requires more elaborate workflows [32], has not yet been investigated within this framework.…”

Electron-phonon scattering from Green's function transport combined with molecular dynamics: Applications to mobility predictions

“…Also, the construction of the perturbed Hamiltonian assumes that the screening is linear such that a change in Hamiltonian from a sum of single atom displacements is the same as the change in Hamiltonian from the summed displacements. This has known limitations for, e.g., polar materials where the long-wavelength Fröhlich interaction is not correctly included [39]. Note that this is not a limitation in the BTE approach, but rather the way we calculate the electron-phonon coupling from finite displacements of individual atoms.…”

First-principles mode-by-mode analysis for electron-phonon scattering channels and mean free path spectra in GaAs

“…Very recently Zhou and Bernardi reported a related first-principles calculation of electron mobility in GaAs based on RTA [74]. According to the Note Added they made, their work has improved, particularly, the convergence with respect to k-and q-point meshes and smearing technique used in calculations.…”