TY - JOUR

T1 - Calculation of dopant solubilities and phase diagrams of X-Pb-Se (X = Br, Na) limited to defects with localized charge

AU - Bajaj, Saurabh

AU - Wang, Heng

AU - Doak, Jeff W.

AU - Wolverton, Chris

AU - Jeffrey Snyder, G.

N1 - Funding Information:
This work was supported by the Department of Energys Basic Energy Sciences program - the Materials Project - under Grant No. EDCBEE. Work at Lawrence Berkeley, through discussions with Qimin Yan, Mark Asta, and Jeff Neaton, was supported by the Office of Science of the U.S. Department of Energy under Contract No. DEAC02-05CH11231. J. W. D. and C.W. acknowledge support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Grant DEFG02-07ER46433. The authors acknowledge the Chemical Engineering Cluster at Texas A&M University and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy, for providing computing resources useful in conducting the research reported in this work. The figures in this article have been created using the LevelScheme scientific figure preparation system.40

PY - 2016/3/7

Y1 - 2016/3/7

N2 - The control of defects, particularly impurities, to tune the concentrations of electrons and holes is of utmost importance in the use of semiconductor materials. To estimate the amount of dopant that can be added to a semiconductor without precipitating secondary phases, a detailed phase diagram is needed. The ability of ab initio computational methods to predict defect stability can greatly accelerate the discovery of new semiconductors by calculating phase diagrams when time-consuming experimental ones are not available. DFT defect energy calculations are particularly successful in identifying doping strategies by determining the energy of multiple defect charge states in large band gap semiconductors and insulators. In metals, detailed phase diagrams can be determined from such calculations but only one, uncharged defect is needed. In this work, we have calculated dopant solubilities of Br and Na in the thermoelectric material PbSe by mapping its solvus boundaries in different regions of the respective ternary phase diagrams using DFT defect energy calculations. The narrow gap PbSe provides an example where defects with nominal charge state (based on valence counting) have properly-localized charge states. However, defects with unexpected charge states produce delocalized electrons, which are then, in effect, defects with the expected charge state. Simply applying the methods for calculating multiple defect charge states in PbSe and treating them as separate defects fails to predict properties measured by experiments. Performing thermodynamic calculations using only the expected charge states, excluding others, enables accurate prediction of experimentally measured doping efficiencies and phase diagrams. Identifying which defect charge states to include in thermodynamic calculations will expedite the use of such calculations for other semiconductors in understanding phase diagrams and devising effective doping strategies.

AB - The control of defects, particularly impurities, to tune the concentrations of electrons and holes is of utmost importance in the use of semiconductor materials. To estimate the amount of dopant that can be added to a semiconductor without precipitating secondary phases, a detailed phase diagram is needed. The ability of ab initio computational methods to predict defect stability can greatly accelerate the discovery of new semiconductors by calculating phase diagrams when time-consuming experimental ones are not available. DFT defect energy calculations are particularly successful in identifying doping strategies by determining the energy of multiple defect charge states in large band gap semiconductors and insulators. In metals, detailed phase diagrams can be determined from such calculations but only one, uncharged defect is needed. In this work, we have calculated dopant solubilities of Br and Na in the thermoelectric material PbSe by mapping its solvus boundaries in different regions of the respective ternary phase diagrams using DFT defect energy calculations. The narrow gap PbSe provides an example where defects with nominal charge state (based on valence counting) have properly-localized charge states. However, defects with unexpected charge states produce delocalized electrons, which are then, in effect, defects with the expected charge state. Simply applying the methods for calculating multiple defect charge states in PbSe and treating them as separate defects fails to predict properties measured by experiments. Performing thermodynamic calculations using only the expected charge states, excluding others, enables accurate prediction of experimentally measured doping efficiencies and phase diagrams. Identifying which defect charge states to include in thermodynamic calculations will expedite the use of such calculations for other semiconductors in understanding phase diagrams and devising effective doping strategies.

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U2 - 10.1039/c5tc03970c

DO - 10.1039/c5tc03970c

M3 - Article

AN - SCOPUS:84959432361

VL - 4

SP - 1769

EP - 1775

JO - Journal of Materials Chemistry C

JF - Journal of Materials Chemistry C

SN - 2050-7526

IS - 9

ER -