Phonon-limited electron mobility in Si, GaAs and GaP with exact treatment of dynamical quadrupoles

We describe a new approach to compute the electron-phonon self-energy and carrier mobilities in semiconductors. Our implementation does not require a localized basis set to interpolate the electron-phonon matrix elements, with the advantage that computations can be easily automated. Scattering potentials are interpolated on dense $\mathbf{q}$ meshes using Fourier transforms and ab initio models to describe the long-range potentials generated by dipoles and quadrupoles. To reduce significantly the computational cost, we take advantage of crystal symmetries and employ the linear tetrahedron method and double-grid integration schemes, in conjunction with filtering techniques in the Brillouin zone. We report results for the electron mobility in Si, GaAs, and GaP obtained with this new methodology

ABINIT: Overview and focus on selected capabilities

Paper published as part of the special topic on Electronic Structure SoftwareABINIT is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe–Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the “temperaturedependent effective potential” approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the associated capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite electric fields; properties at nuclei (electric field gradient, Mössbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calculations of response to strain perturbation (elastic constants and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temperature dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calculations (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library LIBPAW. ABINIT has strong links with many other software projects that are briefly mentioned.This work (A.H.R.) was supported by the DMREF-NSF Grant No. 1434897, National Science Foundation OAC-1740111, and U.S. Department of Energy DE-SC0016176 and DE-SC0019491 projects. N.A.P. and M.J.V. gratefully acknowledge funding from the Belgian Fonds National de la Recherche Scientifique (FNRS) under Grant No. PDR T.1077.15-1/7. M.J.V. also acknowledges a sabbatical “OUT” grant at ICN2 Barcelona as well as ULiège and the Communauté Française de Belgique (Grant No. ARC AIMED G.A. 15/19-09). X.G. and M.J.V. acknowledge funding from the FNRS under Grant No. T.0103.19-ALPS. X.G. and G.-M. R. acknowledge support from the Communauté française de Belgique through the SURFASCOPE Project (No. ARC 19/24-057). X.G. acknowledges the hospitality of the CEA DAM-DIF during the year 2017. G.H. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Materials Project Program No. KC23MP). The Belgian authors acknowledge computational resources from supercomputing facilities of the University of Liège, the Consortium des Equipements de Calcul Intensif (Grant No. FRS-FNRS G.A. 2.5020.11), and Zenobe/CENAERO funded by the Walloon Region under Grant No. G.A. 1117545. M.C. and O.G. acknowledge support from the Fonds de Recherche du Québec Nature et Technologie (FRQ-NT), Canada, and the Natural Sciences and Engineering Research Council of Canada (NSERC) under Grant No. RGPIN-2016-06666. The implementation of the libpaw library (M.T., T.R., and D.C.) was supported by the ANR NEWCASTLE project (Grant No. ANR-2010-COSI-005-01) of the French National Research Agency. M.R. and M.S. acknowledge funding from Ministerio de Economia, Industria y Competitividad (MINECO-Spain) (Grants Nos. MAT2016-77100-C2-2-P and SEV-2015-0496) and Generalitat de Catalunya (Grant No. 2017 SGR1506). This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation program (Grant Agreement No. 724529). P.G. acknowledges support from FNRS Belgium through PDR (Grant No. HiT4FiT), ULiège and the Communauté française de Belgique through the ARC project AIMED, the EU and FNRS through M.ERA.NET project SIOX, and the European Funds for Regional Developments (FEDER) and the Walloon Region in the framework of the operational program “Wallonie-2020.EU” through the project Multifunctional thin films/LoCoTED. The Flatiron Institute is a division of the Simons Foundation. A large part of the data presented in this paper is available directly from the Abinit Web page www.abinit.org. Any other data not appearing in this web page can be provided by the corresponding author upon reasonable request.Peer reviewe

First-principles computation of the electronic transport in semiconductors from electron-phonon coupling

First-principles computations have emerged as a formidable tool for characterizing known and new materials and hence accelerating materials discovery. The electronic transport is among the most important properties for many technological applications. Therefore, a correct ab initio description of the transport properties of functional materials is crucial. In this work, we develop a new methodology to compute the intrinsic carrier mobility and other transport properties in semiconductors directly within the Abinit software. The intrinsic transport is limited by the scattering by phonons and requires precise knowledge of the electron-phonon (e-ph) coupling in the material. In semiconductors and insulators, the e-ph coupling is largely influenced by long-range interactions that have to be taken into account for accurate physical results. We go beyond the state-of-the-art dipolar Fröhlich interactions and include the treatment of quadrupolar fields in the first-principles e-ph coupling matrix elements in semiconductors. We apply our formalism to Si (nonpolar), GaAs, and GaP (polar) and demonstrate that electron mobilities show large errors if dynamical quadrupoles are not properly treated. We also inspect the particular case where the e-ph coupling is so strong that the carriers self-localize and form small polarons. In the framework of transparent conducting oxides (TCOs), we demonstrate using well-known physical models that, in certain circumstances, materials exhibiting transport by small polarons offer a better combination of transparency and conductivity than materials conducting through band transport. We link this surprising finding to the fundamentally different physics of optical absorption for band carriers and small polarons. Our work rationalizes the good performances of recently emerging small-polaron Cr-based p-type TCOs and outlines design principles for the development of high-performance TCOs based on transport by small polarons. This opens new avenues for the discovery of high-performance TCOs especially p-type.(FSA - Sciences de l'ingénieur) -- UCL, 202

Perovskite Sr-doped LaCrO3 : an ab initio study

In this dissertation, the electronic and crystallographic structures of the perovskite Sr-doped LaCrO3 (La(1-x)Sr(x)CrO3) are theoretically investigated. It is a new p-type transparent conductive oxide (TCO), the Sr atoms replacing La ones to create holes as charge carriers. This material could lead to new routes for the design of future efficient p-type TCOs. Indeed, experimental measures show that the carrier transport may be due to small-polaron hopping in La(1-x)Sr(x)CrO3. This phenomenon is usually not wanted for practical applications because of the low effective mass of the carriers, but in this case the conductivity of the material keeps a high value thanks to the high doping levels that are achieved. The purpose of the ab initio computations was thus to find these polarons in the studied materials, and to characterize their electronic properties. Computations were realized using GGA+U with the ABINIT package. It appeared that polarons are indeed present in this material in the case of x = 0.25 and progressively disappear when x increases. There is a transition smearing temperature T∗, a priori different for each oxide, above which the material goes from the polaronic state to a metallic one. It has been possible to evaluate the difference of energy between the two states for x = 0.25 to about 63 meV (the polaronic state being the most stable of the two). This is nevertheless a rough approximation, and a more precise value could be obtained with a deeper analysis. The study led to the following hypothesis. Under a given fraction x∗ of Sr (close to 0.65 according to experiments), the polaronic state would be more stable than the metallic one. Above x∗ , the opposite would be true. In other words, a high concentration of Cr(4+) atoms would favour the metallic state (SrCrO3 having its Cr atoms in the Cr(4+) state, while LaCrO3 has its Cr atoms in the Cr(3+) state). This has been observed for x = 1. The difference of energy between the two structures in the case of SrCrO 3 has been approximated to 43 meV, the metallic one being the most stable state. In order to test this assumption (the existence of a x∗), many computations should be run for different values of x, in order to be able to compute the difference of energy between the insulating and the metallic states in each case.Master [120] : ingénieur civil physicien, Université catholique de Louvain, 201

High-performance transparent conducting oxides through small-polaron transport

Transparent conducting oxides (TCOs) are essential to many technologies including solar cells and transparent electronics. The search for high-performance n- or p-type TCOs has mainly focused on materials offering transport through band carriers instead of small polarons. In this work, we break this paradigm and demonstrate using well-known physical models that, in certain circumstances, TCOs exhibiting transport by small polarons offer a better combination of transparency and conductivity than materials conducting through band transport. We link this surprising finding to the fundamentally different physics of optical absorption for band and polaronic carriers. Our work rationalizes the good performances of recently emerging small-polaronic Cr-based p-type TCOs such as Sr-doped LaCrO3 and outlines design principles for the development of high-performance TCOs based on transport by small polarons. This opens new avenues for the discovery of high-performance TCOs especially p-type

Assessing the quality of relaxation-time approximations with fully automated computations of phonon-limited mobilities

The mobility of carriers, as limited by their scattering with phonons, can now routinely be obtained from first-principles electron-phonon coupling calculations. However, so far, most computations have relied on some form of simplification of the linearized Boltzmann transport equation based on either the self-energy or the momentum relaxation-time or constant relaxation-time approximations. Here, we develop a high-throughput infrastructure and an automatic workflow and we compute 67 phonon-limited mobilities in semiconductors. We compare the results resorting to the approximations with the exact iterative solution. We conclude that the approximate values may deviate significantly from the exact ones and are thus not reliable. Given the minimal computational overhead, our paper encourages reliance on this exact iterative solution

Indirect light absorption model for highly strained silicon infrared sensors

The optical properties of silicon can be greatly tuned by applying strain and opening new perspectives, particularly in applications where infrared is key. In this work, we use a recent model for the indirect light absorption of silicon and include the effects of tensile and compressive uniaxial strains. The model is based on material properties such as the bandgap, the conduction and valence band density-of-states effective masses, and the phonon frequencies, which are obtained from first principles including strain up to +2% along the [110] and [111] directions. We show that the limit of absorption can increase from 1.14 (1.09) to 1.35 $\mu$m (0.92 eV) under 2% strain and that the absorption increases by a factor of 55 for the zero-strain cutoff wavelength of 1.14 $\mu$m when a 2% compressive strain is applied in the [110] direction. We demonstrate that this effect is mainly due to the impact of strain on the electronic bandgaps of silicon, directly followed by the valence band density-of-states effective mass.Comment: Published in Journal of Applied Physics (4 August 2021

Transparent conducting materials discovery using high-throughput computing

Transparent conducting materials (TCMs) are required in many applications from solar cells to transparent electronics. Developing high performance materials combining the antagonistic properties of transparency and conductivity has been challenging especially for p-type materials. Recently, high-throughput ab initio computational screening has emerged as a formidable tool for accelerating materials discovery. In this review, we discuss how this approach has been applied for identifying TCMs. We provide a brief overview of the different materials properties of importance for TCMs (e.g., dopability, effective mass, and transparency) and present the ab initio techniques available to assess them. We focus on the accuracy of the methodologies as well as their suitability for high-throughput computing. Finally, we review the different high-throughput computational studies searching for new TCMs and discuss their differences in terms of methodologies and main findings