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Title: Effect of intermixing at CdS/CdTe interface on defect properties

Abstract

We investigated the stability and electronic properties of defects in CdTe 1- xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe 1- xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

Authors:
 [1];  [1];  [1];  [2]
  1. National Renewable Energy Laboratory, Golden, Colorado 80401, USA
  2. Beijing Computational Science Research Center, Beijing 100094, China
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:
1293800
Report Number(s):
NREL/JA-5K00-66931
Journal ID: ISSN 0003-6951
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; bond formation; II-VI semiconductors; band gap; defect levels; Jahn Teller effect

Citation Formats

Park, Ji-Sang, Yang, Ji-Hui, Barnes, Teresa, and Wei, Su-Huai. Effect of intermixing at CdS/CdTe interface on defect properties. United States: N. p., 2016. Web. doi:10.1063/1.4959848.
Park, Ji-Sang, Yang, Ji-Hui, Barnes, Teresa, & Wei, Su-Huai. Effect of intermixing at CdS/CdTe interface on defect properties. United States. doi:10.1063/1.4959848.
Park, Ji-Sang, Yang, Ji-Hui, Barnes, Teresa, and Wei, Su-Huai. 2016. "Effect of intermixing at CdS/CdTe interface on defect properties". United States. doi:10.1063/1.4959848.
@article{osti_1293800,
title = {Effect of intermixing at CdS/CdTe interface on defect properties},
author = {Park, Ji-Sang and Yang, Ji-Hui and Barnes, Teresa and Wei, Su-Huai},
abstractNote = {We investigated the stability and electronic properties of defects in CdTe 1- xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe 1- xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.},
doi = {10.1063/1.4959848},
journal = {Applied Physics Letters},
number = 4,
volume = 109,
place = {United States},
year = 2016,
month = 7
}
  • We investigated the stability and electronic properties of defects in CdTe{sub 1−x}S{sub x} that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, V{sub Cd}, and Te on Cd antisite, Te{sub Cd}, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of V{sub Cd} and Te{sub Cd} become close to the valence band maximum when the defect has more S atoms in their local environment, thusmore » improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe{sub 1−x}S{sub x} increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.« less
  • CdS/CdTe structures deposited on different substrates are analyzed using transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), optical transmission, atomic force microscopy (AFM), X-ray diffraction (XRD) and photoluminescence (PL). The microstructure of CdTe was found to be independent of CdS crystallinity, and the structural defects at CdS/CdTe interface are generated principally by the lattice mismatch between CdS and CdTe. The interdiffusion at the CdS/CdTe interface was found to be a function of substrate temperature and CdCl{sub 2} heat treatment. {copyright} {ital 1996 American Institute of Physics.}
  • A study of the CdS/CdTe interface was performed on glass/SnO{sub 2}/CdS/CdTe device structures. CdS layers were deposited by chemical solution growth to a thickness of 80--100 nm, and CdTe was deposited by close-spaced sublimation at substrate temperatures of 500, 550, and 600 C. Post-deposition CdCl{sub 2} heat treatment was performed at 400 C. Samples were analyzed by optical spectroscopy, secondary ion mass spectrometry (SIMS), spectral response, and current-voltage measurements. SIMS analysis shows that the intermixing of CdS and CdTe is a function of substrate temperature and post-deposition CdCl{sub 2} heat treatment. The degree of intermixing increases with increases in substratemore » temperature and the intensity of CdCl{sub 2} heat treatment. Optical analysis and X-Ray diffraction data show that the phases of CdS{sub x}Te{sub 1{minus}x} are also a function of the same parameters. Formation of a Te-rich CdS{sub x}Te{sub 1{minus}x} alloy is favored for films deposited at higher substrate temperatures. Spectral response of the devices is affected by the degree of alloying at the interface. The degree of alloying is indicated by simultaneous changes in long wavelength response (due to the formation of lower bandgap intermixed CdS{sub x}Te{sub 1{minus}x}) and the short wavelength response (due to the change in CdS thickness). Device performance is heavily influenced by alloying at the interface. With optimized intermixing, improvements in V{sub oc} and diode quality factors are observed in the resulting devices.« less
  • We have investigated the effect of the CdS/CdTe interdiffusion on the properties of the CdTe films and the CdS/CdTe cell performance. Sulfur (S) diffusion into the CdTe films leads to a decreased defect density in the films, improvement of cell performance, and possibly to the increase of the carrier lifetime in the films. Cell performance is improved with the increase of the amount of S in the CdTe films. S diffusion into CdTe also deteriorates the uniformity of the CdS window layers, resulting in worse cell performance. Based on this study, we propose a processing method to improve cell performance.more » {copyright} {ital 1999 American Institute of Physics.}« less