Formation of CdZnS thin films by Zn diffusion

• Published in: Journal of physics. D, Applied physics Vol. 39; no. 15; pp. 3221 - 3225
• Main Authors: Dzhafarov, T D, Ongul, F, Karabay, I
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 07.08.2006; Institute of Physics
• Subjects: Condensed matter: structure, mechanical and thermal properties; Diffusion; interface formation; Exact sciences and technology; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin films; Zinc sulfides; X ray fluorescence; Cadmium sulfides; XRD; Interface reaction; Absorption spectra; Melting points; Thermal annealing; Dispersive spectrometry; Depth profiles; Concentration distribution
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/39/15/001

The structural, composition and optical absorption properties of Cd1-xZnxS (CdZnS) thin films fabricated by the reactive diffusion of Zn in CdS have been investigated. These ternary compounds were characterized by x-ray diffraction (XRD), energy dispersive x-ray fluorescence and optical absorption measurements. It is established that thermal annealing of Zn/CdS structure at temperature (400 deg C) lower than the melting point of Zn (418 deg C) results in the concentration distribution of Zn in CdS film described by an erfc-curve (D = 5 X 10-14 cm2 s-1) and characterizing the free impurity diffusion from a constant source. In contrast to this, the concentration profile of Zn in CdS film at higher annealing temperature (570 deg C) is not described by the erfc-curve and shows a nearly stepped form, which is characteristic of reactive diffusion. XRD patterns of Zn/CdS structures annealed at 570 deg C showed diffraction peaks of ternary CdZnS compounds. Analysis of the absorption spectrum of such films indicates formation of CdZnS composition with the largest value of energy band gap up to 2.64 eV, exceeding the band gap of CdS (2.43 eV). It is concluded that interdiffusion in Zn/CdS structures at temperatures exceeding the melting point of Zn was accompanied by formation of Cd1-xZnxS ternary compounds. The band gap of this variable band structure changes from 2.64 eV in the near surface region to 2.43 eV (CdS) in the inner region of the film.