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Thin-Film Cadmium Sulfide/Cadmium Telluride Alloys

Published online by Cambridge University Press:  10 February 2011

D. G. Jensen
Affiliation:
Institute of Energy Conversion, University of Delaware United States Department of Energy, University Center of Excellence for Photovoltaics Research and Education, Newark, DE 19716
B. E. McCandless
Affiliation:
Institute of Energy Conversion, University of Delaware United States Department of Energy, University Center of Excellence for Photovoltaics Research and Education, Newark, DE 19716
R. W. Birkmire
Affiliation:
Institute of Energy Conversion, University of Delaware United States Department of Energy, University Center of Excellence for Photovoltaics Research and Education, Newark, DE 19716
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Abstract

Thin films of CdTel-xSx with bulk atomic compositions, x≡[S]/([S]+[Te]), ranging from 0 to 0.45 were deposited by vacuum co-evaporation of CdTe and CdS with substrate temperatures of 200 and 250°C. X-ray diffraction analysis revealed that films with x < 0.3 were predominately single phase having the zincblende structure. Films with 0.35 < x < 0.45 contained the wurtzite modification. Lattice parameter determination indicated that each phase exists with compositions well within the miscibility gap shown on published equilibrium phase diagrams. The variation of the optical band gap with x was determined by measuring transmission and reflection of the films. Heat treatment at 415°C in the presence of CdC12 caused the films to segregate into two phases consistent with the phase diagram. If the CdCl2 is assumed to only promote the phase segregation process, then the compositions of the two phases after heat treatment may be taken as measurements of the solubility limits of S in CdTe and Te in CdS respectively. The solubility limit of S in CdTe was thus determined to be 5.8% at 415°C which is the temperature used for the common CdC12 treatment of CdTe-based solar cells. An analysis of CdTe/CdS solar cell device structures shows that the atomic composition of alloys created by interdiffusion are consistent with these solubility limits.

Type
Research Article
Copyright
Copyright © Materials Research Society 1996

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