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Title: Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study

Abstract

Here, we apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σ o) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta 2O 5, where each reference contains a single, neutral O vacancy center (V O 0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta 2O x σ o, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta 2O x σ o, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO 3 group formation, especially in the low σ o reference. While N applications to dope and passivate oxides are prevalent, we also found that N exacerbates the stochasticity of σ o we sought to mitigate; sensitivity to the N insertion site andmore » some propensity to form N-O bond chemistries appear responsible. Finally, we use direct first-principles predictions of σ o to explore feasible Ta 2O 5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.« less

Authors:
 [1];  [1];  [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1361046
Alternate Identifier(s):
OSTI ID: 1366554
Report Number(s):
SAND2017-3842J
Journal ID: ISSN 0021-8979; 652423
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 21; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Bondi, Robert J., Fox, Brian P., and Marinella, Matthew J.. Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study. United States: N. p., 2017. Web. doi:10.1063/1.4983850.
Bondi, Robert J., Fox, Brian P., & Marinella, Matthew J.. Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study. United States. doi:10.1063/1.4983850.
Bondi, Robert J., Fox, Brian P., and Marinella, Matthew J.. Thu . "Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study". United States. doi:10.1063/1.4983850.
@article{osti_1361046,
title = {Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study},
author = {Bondi, Robert J. and Fox, Brian P. and Marinella, Matthew J.},
abstractNote = {Here, we apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we also found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. Finally, we use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.},
doi = {10.1063/1.4983850},
journal = {Journal of Applied Physics},
number = 21,
volume = 121,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}

Journal Article:
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  • We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta{sub 2}O{sub x} (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V{sub O}{sup n}; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V{sub O}{sup 0} prefers equatorial O sites, while V{sub O}{sup 1+} and V{sub O}{sup 2+} are energetically preferred in the O cap sites of TaO{sub 7} polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta{sub 2}O{submore » x} thin films (0.18 ≤ x ≤ 4.72) and bulk Ta{sub 2}O{sub 5} powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta{sub 2}O{sub 5} electronic structure provide further theoretical basis to substantiate V{sub O}{sup 0} as a donor dopant in Ta{sub 2}O{sub 5}. Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V{sub O}{sup n} in Ta{sub 2}O{sub 5}.« less
  • First-principles calculations of electrical conductivity (σ{sub o}) are revisited to determine the atomistic origin of its stochasticity in a distribution generated from sampling 14 ab-initio molecular dynamics configurations from 10 independently quenched models (n = 140) of substoichiometric amorphous Ta{sub 2}O{sub 5}, where each structure contains a neutral O monovacancy (V{sub O}{sup 0}). Structural analysis revealed a distinct minimum Ta-Ta separation (dimer/trimer) corresponding to each V{sub O}{sup 0} location. Bader charge decomposition using a commonality analysis approach based on the σ{sub o} distribution extremes revealed nanostructural signatures indicating that both the magnitude and distribution of cationic charge on the Ta subnetwork havemore » a profound influence on σ{sub o}. Furthermore, visualization of local defect structures and their electron densities reinforces these conclusions and suggests σ{sub o} in the amorphous oxide is best suppressed by a highly charged, compact Ta cation shell that effectively screens and minimizes localized V{sub O}{sup 0} interaction with the a-Ta{sub 2}O{sub 5} network; conversely, delocalization of V{sub O}{sup 0} corresponds to metallic character and high σ{sub o}. The random network of a-Ta{sub 2}O{sub 5} provides countless variations of an ionic configuration scaffold in which small perturbations affect the electronic charge distribution and result in a fixed-stoichiometry distribution of σ{sub o}; consequently, precisely controlled and highly repeatable oxide fabrication processes are likely paramount for advancement of resistive memory technologies.« less
  • In this study, first-principles calculations of electrical conductivity (σ o) are revisited to determine the atomistic origin of its stochasticity in a distribution generated from sampling 14 ab-initio molecular dynamics configurations from 10 independently quenched models (n = 140) of substoichiometric amorphous Ta 2O 5, where each structure contains a neutral O monovacancy (V O 0). Structural analysis revealed a distinct minimum Ta-Ta separation (dimer/trimer) corresponding to each V O 0 location. Bader charge decomposition using a commonality analysis approach based on the σ o distribution extremes revealed nanostructural signatures indicating that both the magnitude and distribution of cationic chargemore » on the Ta subnetwork have a profound influence on σ o. Furthermore, visualization of local defect structures and their electron densities reinforces these conclusions and suggests σ o in the amorphous oxide is best suppressed by a highly charged, compact Ta cation shell that effectively screens and minimizes localized V O 0 interaction with the a-Ta 2O 5 network; conversely, delocalization of V O 0 corresponds to metallic character and high σ o. The random network of a-Ta 2O 5 provides countless variations of an ionic configuration scaffold in which small perturbations affect the electronic charge distribution and result in a fixed-stoichiometry distribution of σ o; consequently, precisely controlled and highly repeatable oxide fabrication processes are likely paramount for advancement of resistive memory technologies.« less
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