Efficient stochastic generation of special quasirandom structures

Walle, Axel van de; Tiwary, Pratyush; Jong, M. de; Olmsted, David L.; Asta, Mark; Dick, A.; Shin, Dongwon; Wang, Yi; Chen, Lei; Liu, Zhe

doi:10.1016/j.calphad.2013.06.006

Cited by 1,164 publications

(521 citation statements)

References 22 publications

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“…To model the alloy structures, we employed the special quasi-random structures (SQSs) 43,44 as generated with the mcsqs utility as implemented in the ATAT. 45 Relatively large 256-atom SQS supercells were chosen such to include low alloy compositions. In order to facilitate the Brillouin zone sampling in the density functional theory (DFT) calculations, we have chosen the supercells in a shape close to a cube, and search for SQS structures such that the pair correlation functions agree with the ideal random alloy up to the 8th nearest neighbor in the cation sublattice for all compositions considered.…”

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confidence: 99%

Pathway to oxide photovoltaics via band-structure engineering of SnO

et al. 2016

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The prospects of scaling current photovoltaic technologies to terawatt levels remain uncertain. All-oxide photovoltaics could open rapidly scalable manufacturing routes, if only oxide materials with suitable electronic and optical properties were developed. A potential candidate material is tin monoxide (SnO), which has exceptional doping and transport properties among oxides, but suffers from a low absorption coefficient due to its strongly indirect band gap. Here, we address this shortcoming of SnO by band-structure engineering through isovalent but heterostructural alloying with divalent cations (Mg, Ca, Sr, Zn). Using first-principles calculations, we show that suitable band gaps and optical properties close to that of direct semiconductors are achievable in such SnO based alloys. Due to the defect tolerant electronic structure of SnO, the dispersive band-structure features and comparatively small effective masses are preserved in the alloys. Initial Sn 1−x Zn x O thin films deposited by sputtering exhibit crystal structure and optical properties in accord with the theoretical predictions, which confirms the feasibility of the alloying approach. Thus, the implications of this work are important not only for terawatt scale photovoltaics, but also for other large-scale energy technologies where defect-tolerant semiconductors with high quality electronic properties are required.

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Pathway to oxide photovoltaics via band-structure engineering of SnO

et al. 2016

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“…37 To assess the validity of this approach for In x Al 1-x N, we generated periodic SQSs models of 96 atoms with the Alloy Theoretic Automated Toolkit (ATAT) software and calculated the corresponding band gaps. [38][39][40][41][42][43] As shown in Fig. 1, we found that SQSs systematically overestimate the experimental band gaps with a bowing parameter of 2.93 eV, much smaller than the experimental one of about ∼ 6 eV.…”

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confidence: 83%

Oxygen DX center in In0.17Al0.83N: Nonradiative recombination and persistent photoconductivity

Meli

Miceli

Pasquarello

2017

Applied Physics Letters

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Using a hybrid density-functional scheme, we address the O impurity substitutional to N (O N ) in In 0.17 Al 0.83 N. Our modelling supports In clustering to account for the strong band-gap bowing observed in In x Al 1-x N alloys. To study the O N defect in In 0.17 Al 0.83 N alloys, we therefore consider a model containing an In cluster and find that the most stable configuration shows four In nearest neighbors. We show that such a O N defect forms a DX center and gives rise to two defect levels at 0.70 and 0.41 eV below the conduction band edge, in good agreement with experiment. The calculated defect energetics entail a fast nonradiative recombination upon photoexcitation at room temperature and account for the observation of persistent photoconductivity at low temperature.PACS numbers: 71.55. Eq,61.72.uj In the last decades, In x Al 1-x N has attracted a great deal of interest for its possible applications in electronic and optoelectronic devices. 1-3 In particular, In 0.17 Al 0.83 N is nearly lattice matched to GaN and can be used to realize strain-free heterostructures. 4,5 Applications include distributed Bragg reflectors, thick cladding layers in edge emitting lasers, waveguides exploiting the large difference in refractive indices between InAlN and GaN, and high-electron mobility transistors (HEMTs). [6][7][8] To control the electronic properties of these materials, it is important to understand the role of impurities. Upon growth through metalorganic vapor phase epitaxy (MOVPE), it is known that considerable concentrations of oxygen and carbon impurities are incorporated. 8 Experimental investigations have identified various defect states with activation energies ranging between 200 and 500 meV. 9-11 However, their origin has been difficult to ascertain and it has remained unclear whether these states relate to point defects or to dislocations. More recently, defect states have been measured at 68 meV and 270 meV and tentatively assigned to oxygen on the basis of their concentration. 12 The observation of persistent photoconductivity (PPC) effects has been taken as an indication supporting this interpretation, 12 as oxygen is known to give rise to DX centers in AlN. 13 In this Letter, we study the oxygen impurity substitutional to nitrogen (O N ) in In 0.17 Al 0.83 N through densityfunctional-theory calculations. We find that O N gives defect levels that are in agreement with experimental observations. These impurities behave like DX centers and can explain the origin of the persistent photoconductivity effects.In our calculations, we make use of the semilocal density functional introduced by Perdew, Burke, and Ernzerhof (PBE), 14 and of the hybrid functional introduced by Heyd, Scuseria, and Ernzerhof (HSE). 15,16 In the latter, the fraction of Fock exchange is set to α = 0.37 for AlN and to α = 0.19 for InN, in order to reproduce their experimental band gaps. For intermediate In x Al 1-x N alloys, the mixing coefficient α is linearly interpolated.We use normconserving pseudopotentials to treat corev...

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“…The value η max = 0.05 was chosen after extensive convergence testing and is located near a local plateau of the TOECs as a function of strain 25,26 . In general, both the SOEC's and TOEC's obtained from DFT do not precisely obey the desired symmetry dictated by the underlying crystal point group 18,[27][28][29][30][31] . The correct symmetry is therefore restored by performing an average over the pertinent point group operations.…”

Section: Methodology a Wallace Formalism And Elastic Instabilitiesmentioning

confidence: 99%

Ideal strength and ductility in metals from second- and third-order elastic constants

et al. 2017

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Under tensile loading the ideal strength of a solid is governed by mechanical instabilities corresponding to failure in tension or shear, indicative of intrinsically brittle or ductile behavior, respectively. Ideal-strength first-principles calculations are performed in this work on several hexagonalclose-packed (hcp) and body-centered-cubic (bcc) metals. It is shown that some metals fail in tension under uniaxial loading, whereas others fail in shear. The observed behavior is rationalized with a simple analytical model based on second-order and third-order elastic constants. This formalism correctly predicts the failure mode of all but one of the metals studied in this work and leads to fundamental new insights into why some classes of metals are intrinsically brittle or ductile. Further, for the transition metals, filling of the d-bands is shown to correlate with the type of mechanical instability encountered, thus providing new insights into the effect of alloying on the intrinsic mechanical behavior of hcp and bcc metals.

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Efficient stochastic generation of special quasirandom structures

Cited by 1,164 publications

References 22 publications

Pathway to oxide photovoltaics via band-structure engineering of SnO

Pathway to oxide photovoltaics via band-structure engineering of SnO

Oxygen DX center in In0.17Al0.83N: Nonradiative recombination and persistent photoconductivity

Ideal strength and ductility in metals from second- and third-order elastic constants

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