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Scaling tests of a new algorithm for DFT hybrid-functional calculations on Trinity Haswell

Wright, Alan F.; Modine, N.A.

We show scaling results for materials of interest in Sandia Radiation-Effects and High-Energy-Density-Physics Mission Areas. Each timing is from a self-consistent calculation for bulk material. Two timings are given: (1) walltime for the construction of the CR exchange operator (Exchange-Operator) and (2) walltime for everything else (non-Exchange-Operator).

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TYPE Other Report YEAR 2017
OSTIDOI

Compact Models for Defect Diffusivity in Semiconductor Alloys

Wright, Alan F.; Modine, N.A.; Lee, Stephen R.; Foiles, Stephen M.

Predicting transient effects caused by short - pulse neutron irradiation of electronic devices is an important part of Sandia's mission. For example , predicting the diffusion of radiation - induced point defects is needed with in Sandia's Qualification Alternative to the Sandia Pulsed Reactor (QASPR) pro gram since defect diffusion mediates transient gain recovery in QASPR electronic devices. Recently, the semiconductors used to fabricate radiation - hard electronic devices have begun to shift from silicon to III - V compounds such as GaAs, InAs , GaP and InP . An advantage of this shift is that it allows engineers to optimize the radiation hardness of electronic devices by using alloy s such as InGaAs and InGaP . However, the computer codes currently being used to simulate transient radiation effects in QASP R devices will need to be modified since they presume that defect properties (charge states, energy levels, and diffusivities) in these alloys do not change with time. This is not realistic since the energy and properties of a defect depend on the types of atoms near it and , therefore, on its location in the alloy. In particular, radiation - induced defects are created at nearly random locations in an alloy and the distribution of their local environments - and thus their energies and properties - evolves with time as the defects diffuse through the alloy . To incorporate these consequential effects into computer codes used to simulate transient radiation effects, we have developed procedures to accurately compute the time dependence of defect energies and properties and then formulate them within compact models that can be employed in these computer codes. In this document, we demonstrate these procedures for the case of the highly mobile P interstitial (I P ) in an InGaP alloy. Further dissemination only as authorized to U.S. Government agencies and their contractors; other requests shall be approved by the originating facility or higher DOE programmatic authority.

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TYPE SAND Report YEAR 2017
OSTIDOI

Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

Physical Review B - Condensed Matter and Materials Physics

Wright, Alan F.; Modine, N.A.

A recently developed bounds-analysis approach has been used to interpret density-functional-theory (DFT) results for the As and Ga antisites in GaAs. The bounds analysis and subsequent processing of DFT results for the As antisite yielded levels - defined as the Fermi levels at which the defect charge state changes - in very good agreement with measurements, including the -1/0 level which is within 0.1 eV of the conduction-band edge. Good agreement was also obtained for the activation energies to transform the AsGa from its metastable state to its stable state. For the Ga antisite, the bounds analysis revealed that the -1 and 0 charge states are hole states weakly bound to a localized -2 charge state. The calculated levels are in good agreement with measurements.

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TYPE Journal Article YEAR 2015
ScopusOSTIDOI

Density Functional Theory Calculations of Activation Energies for Non-radiative Carrier Capture by Deep Defect Levels in Semiconductors

Sandia journal manuscript; Not yet accepted for publication

Modine, N.A.; Wright, Alan F.; Lee, Stephen R.

Carrier recombination due to defects can have a major impact on device performance. The rate of defect-induced carrier recombination is determined by both defect levels and carrier capture cross-sections. Kohn-Sham density functional theory (DFT) has been widely and successfully used to predict defect levels in semiconductors and insulators, but only recently has work begun to focus on using DFT to determine carrier capture cross-sections. Lang and Henry worked out the fundamental theory of carrier-capture cross-sections in the 1970s and showed that, in most cases, room temperature carrier-capture cross-sections differ between defects primarily due to differences in the carrier capture activation energies. Here, we present an approach to using DFT to calculate carrier capture activation energies that does not depend on perturbation theory or an assumed configuration coordinate, and we demonstrate this approach for the -3/-2 level of the Ga vacancy in wurtzite GaN.

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TYPE Journal Article YEAR 2014
OSTI
Results 1–25 of 54
Results 1–25 of 54