Journal
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS
Volume 136, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jpcs.2019.109154
Keywords
Chalcogenide; Thin films; XAFS (XANES and EXAFS)
Funding
- CONACYT, Mexico [169108]
- US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
- LANNBIO, CINVESTAV, Mexico [FOMIX-YUCATAN 2008-108160]
- CONACYT LAB-2009-01 [123913]
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X-ray absorption fine structure (XAFS) spectroscopy was used to address both the local atomic structure and the local electronic structure around Zn, Co, and S in Co-doped ZnS thin films. X-ray absorption near-edge spectroscopy (XANES) revealed changes in the strong pre-edge feature of the S K-edge spectra that depend on the Co concentration and are related to atomic bound-state transitions through hybridization between 3d transition metal and sp host semiconductor electronic states. These changes reveal intrinsic effects, such as S vacancies and dopant effects. From the Co K-edge XANES spectra, substitution of Co2+ into ZnS is observed. The local atomic structure around the dopant, obtained by XAFS spectroscopy, indicates a reduction of the Co S bond length. Optical analysis shows deep absorption centers or intermediate states in the bandgap, ascribed to d-d transitions in the Co atoms that modify the electronic band structure and cause a decrease in the bandgap as a function of Co concentration. This work provides direct evidence of dopant effects in heavily Co-doped ZnS, including bond distances and Debye-Waller factors, providing key elements to generate a realistic atomic structural model, which is crucial to understand the observed electronic properties of this material.
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