The microscopic response method: Theory of transport for systems with both topological and thermal disorder (original) (raw)
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Phys Rev Lett, 2010
We introduce a theoretical framework for computing transport coefficients for complex materials. As a first example, we resolve long-standing inconsistencies between experiment and theory pertaining to the conductivity and Hall mobility for amorphous silicon and show that the Hall sign anomaly is a consequence of localized states. Next, we compute the AC conductivity of amorphous polyanaline. The formalism is applicable to complex materials involving defects and band-tail states originating from static topological disorder and extended states. The method may be readily integrated with current ab initio methods.
2010
We introduce a theoretical framework for computing transport coefficients for complex materials with extended states, and defect or band-tail states originating from static topological disorder. As a first example, we resolve long-standing inconsistencies between experiment and theory pertaining to the conductivity and Hall mobility for amorphous silicon and show that the Hall sign anomaly is a consequence of localized states. Next, we compute the ac conductivity of amorphous polyaniline. The method may be readily integrated with current ab initio methods.
Phonon driven transport in amorphous semiconductors: transition probabilities
The European Physical Journal B, 2010
Starting from Holstein's work on small polaron hopping, the evolution equations for localized and extended states in the presence of atomic vibrations are systematically derived for an amorphous semiconductor. The transition probabilities are obtained for transitions between all combinations of localized and extended states. For any transition process involving a localized state, the activation energy is not simply the energy difference between the final and initial states; the reorganization energy of atomic configuration is also included as an important part of the activation energy (Marcus form). The activation energy for the transitions between localized states decreases with rising temperature and leads to the Meyer-Neldel rule. The predicted Meyer-Neldel temperatures are consistent with observations in several materials. The computed field-dependence of conductivity agrees with experimental data. The present work suggests that the upper temperature limit of variable range hopping is proportional to the frequency of first peak of phonon spectrum. We have also improved the description of the photocurrent decay at low temperatures. Analysis of the transition probability from an extended state to a localized state suggests that there exists a short-lifetime belt of extended states inside the conduction band or valence band.
First-principles mobility prediction for amorphous semiconductors
Physical Review B, 2022
Carrier mobility in amorphous semiconductors remained unpredictable due to random electronic states in the absence of the long-range order in a lattice structure, although amorphous semiconductors have been investigated over several decades and widely used in diverse electronic devices. In this work, we develop a method to predict mobility of disordered systems by virtue of the first-principles calculation without using any empirical parameters. Quantum transport modeling based on the nonequilibrium Green's function formalism enables us to establish a formula to connect first-principles results with amorphous-phase mobility. Finally, the developed approach is quantitatively validated by comparing the theoretical predictions with previously measured mobilities of amorphous metal oxides (SnO 2 , In 2 O 3 , and ZnO) and amorphous silicon. Localization analysis provides further physical insight into a distinct feature between the amorphous metal oxides and amorphous silicon.
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2009
Using density functional perturbation theory and a full solution of the linearized phonon Boltzmann transport equation (BTE), a parameter-free theory of semiconductor thermal properties is developed. The approximations and shortcomings of previous approaches to thermal conductivity calculations are investigated. The use of empirical interatomic potentials in the BTE approach is shown to give poor agreement with measured values of thermal conductivity. By using the adiabatic bond charge model, the importance of accurate descriptions of phonon dispersions is highlighted. The extremely limited capacity of previous theoretical techniques in the realm of thermal conductivity prediction is highlighted; this is due to a dependence on adjustable parameters. Density functional perturbation theory is coupled with an iterative solution to the full Boltzmann transport equation creating a theoretical construct where thermal conductivity prediction becomes possible. Validation of the approach is ...
Direct method for calculating temperature-dependent transport properties
Physical Review B, 2015
We show how temperature-induced disorder can be combined in a direct way with first-principles scattering theory to study diffusive transport in real materials. Excellent (good) agreement with experiment is found for the resistivity of Cu, Pd, Pt (and Fe) when lattice (and spin) disorder are calculated from first principles. For Fe, the agreement with experiment is limited by how well the magnetization (of itinerant ferromagnets) can be calculated as a function of temperature. By introducing a simple Debye-like model of spin disorder parameterized to reproduce the experimental magnetization, the temperature dependence of the average resistivity, the anisotropic magnetoresistance and the spin polarization of a Ni80Fe20 alloy are calculated and found to be in good agreement with existing data. Extension of the method to complex, inhomogeneous materials as well as to the calculation of other finite-temperature physical properties within the adiabatic approximation is straightforward.
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First principles molecular dynamics is employed to investigate thermal transport in glassy GeTe4, a subsystem of several ternary phase-change materials. As a first result, we found modes localized on a few atoms in the vibrational density of states. The thermal transport is further rationalized by calculating the thermal conductivity for a range of system sizes and shapes via the approachto-equilibrium methodology. By considering the length dependence of the thermal conductivity, we provide evidence of propagative modes with mean free paths as long as 6 nm, i. e. well beyond short range order distances. Extrapolation of our bulk thermal conductivity to macroscopic sizes is in full agreement with the experimental values. Finally, we assess phenomenological models developed for the thermal conductivity of disordered materials, by enriching their intrinsic significance via the insertion in their analytical expression of values obtained via first principles molecular dynamics.
The calculation of transport properties and density of states of disordered solids
European Physical Journal B, 1985
A computational method is presented for the calculation of the conductivity tensor and the density of states of disordered solids. This is a more general and detailed discussion of an algorithm which has been applied to d.c. and a.c. conductivity, Hall effect and density of states of various systems.
Unified Mobility Model for Amorphous Organic Materials
2009 International Conference on Simulation of Semiconductor Processes and Devices, 2009
The influence of temperature, carrier concentration and electric field on the hopping transport in disordered organic semiconductors is studied theoretically, and a simple and accurate analytical model is worked out. The model is based on the concept of percolation in a variable range hopping system and the calculations are worked out exploiting the effective temperature approach. At room temperature the dependence on carrier density plays a major role, whereas at low temperatures or high fields the electric field dependence becomes relevant. Neglecting only one of those effects, depending on the operating conditions, leads to an evident underestimation of the hopping mobility.