Journal
MATERIALS CHEMISTRY AND PHYSICS
Volume 111, Issue 2-3, Pages 475-479Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.matchemphys.2008.04.052
Keywords
transition metal dichalcogenides; piezoreflectance; surface photovoltage spectroscopy; photoconductivity
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Funding
- National Science Council of Taiwan [NSC962112-M-011-001, NSC96-2221-E-011-030, NSC95-2112-M-019-001]
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Single crystals of WS2 doped with gold have been grown by the chemical vapour transport method using iodine as a transporting agent. X-ray diffraction (XRD) pattern analysis revealed presence of mixed three-layer rhombohedral (3R)and two-layer hexagonal (2H) polytypes for the doped crystals while the undoped one shows only 2H form. Hall measurements indicate that the samples are p-type in nature. The doping effects of the materials are characterized by surface photovoltage (SPV), photoconductivity (PC) and piezoreflectance (PzR) measurements. Room temperature SPV and PC spectra reveal a feature located at similar to 60meV below the A exciton and has been tentatively assigned to be an impurity level caused by Au dopant. Excitonic transition energies of the A, B, d and C excitons detected in PzR spectra show red shift due to the presence of a small amount of Au and the broadening parameters of the excitonic transition features increase due to impurity scattering. The values of the parameters that describe the electron (exciton)-phonon interaction of excitonic transitions of A-B are about two times larger than that of d-C excitonic pairs. The possible assignments of the different origins of A-B and d-C excitonic pairs have been discussed. C) 2008 Elsevier B.V. All rights reserved.
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