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Title: Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe

Abstract

Defect formation energies and transition levels are critical in determining doping behavior and recombination in semiconductor applications. Hybrid functionals are often used to overcome the band gap and delocalization errors of standard density-functional theory, and it is tempting to presume that the defect properties are correctly predicted once the hybrid functional mixing parameter reproduces the experimental band gap. However, pronounced spin-orbit coupling (SOC) effects can have an additional important role, which is clearly shown in this work by analyzing SOC effects originating from the Te-p orbitals in CdTe. In this work, we therefore use a hybrid functional that reproduces the experimental band gap when SOC is included, requiring a larger mixing parameter a=0.33 compared to the conventional choice of a=0.25. This hybrid functional was then used to predict defect properties, e.g., formation energy, transition level, and defect equilibrium. For defect states that do not directly involve the Te-p orbitals, such as the Cd interstitial (Cdi), we find that the effect of SOC on the defect levels can be captured by simply considering the SOC-induced band-edge shift. This is not the case for the A center (ClTe-VCd defect pair), where the localized acceptor state formed by Te-p orbitals is more directlymore » affected by the SOC. For this defect, a mixing parameter as large as a=0.40 is required to reproduce the experimental acceptor level. Regarding the implications for photovoltaics, we suggest that the Cdi, which is the dominant compensating donor, could play an important role as a recombination center. While Cdi is usually thought of as a benign shallow donor, our predicted defect levels in the fully band-gap-corrected calculations are deep enough to raise a concern, and we propose a recombination mechanism for electron capture by Cdi.« less

Authors:
 [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1475126
Alternate Identifier(s):
OSTI ID: 1465890
Report Number(s):
NREL/JA-5K00-72123
Journal ID: ISSN 2469-9950; PRBMDO
Grant/Contract Number:  
AC36-08GO28308; DEAC36-08GO28308; EE0006344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 98; Journal Issue: 5; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; hybrid functionals; band gap; spin-orbit coupling; defect formation

Citation Formats

Pan, Jie, Metzger, Wyatt K., and Lany, Stephan. Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe. United States: N. p., 2018. Web. doi:10.1103/PhysRevB.98.054108.
Pan, Jie, Metzger, Wyatt K., & Lany, Stephan. Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe. United States. https://doi.org/10.1103/PhysRevB.98.054108
Pan, Jie, Metzger, Wyatt K., and Lany, Stephan. Wed . "Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe". United States. https://doi.org/10.1103/PhysRevB.98.054108. https://www.osti.gov/servlets/purl/1475126.
@article{osti_1475126,
title = {Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe},
author = {Pan, Jie and Metzger, Wyatt K. and Lany, Stephan},
abstractNote = {Defect formation energies and transition levels are critical in determining doping behavior and recombination in semiconductor applications. Hybrid functionals are often used to overcome the band gap and delocalization errors of standard density-functional theory, and it is tempting to presume that the defect properties are correctly predicted once the hybrid functional mixing parameter reproduces the experimental band gap. However, pronounced spin-orbit coupling (SOC) effects can have an additional important role, which is clearly shown in this work by analyzing SOC effects originating from the Te-p orbitals in CdTe. In this work, we therefore use a hybrid functional that reproduces the experimental band gap when SOC is included, requiring a larger mixing parameter a=0.33 compared to the conventional choice of a=0.25. This hybrid functional was then used to predict defect properties, e.g., formation energy, transition level, and defect equilibrium. For defect states that do not directly involve the Te-p orbitals, such as the Cd interstitial (Cdi), we find that the effect of SOC on the defect levels can be captured by simply considering the SOC-induced band-edge shift. This is not the case for the A center (ClTe-VCd defect pair), where the localized acceptor state formed by Te-p orbitals is more directly affected by the SOC. For this defect, a mixing parameter as large as a=0.40 is required to reproduce the experimental acceptor level. Regarding the implications for photovoltaics, we suggest that the Cdi, which is the dominant compensating donor, could play an important role as a recombination center. While Cdi is usually thought of as a benign shallow donor, our predicted defect levels in the fully band-gap-corrected calculations are deep enough to raise a concern, and we propose a recombination mechanism for electron capture by Cdi.},
doi = {10.1103/PhysRevB.98.054108},
url = {https://www.osti.gov/biblio/1475126}, journal = {Physical Review B},
issn = {2469-9950},
number = 5,
volume = 98,
place = {United States},
year = {2018},
month = {8}
}

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