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STUDIA UNIVERSITATIS BABEŞ-BOLYAI, CHEMIA, LIV, 3, 2009 GROWTH AND CHARACTERISATION OF ZINC-CADMIUM SULPHIDE THIN FILMS WITH SPECIAL OPTICAL PROPERTIES MARIA ŞTEFAN a, b , IOAN BÂLDEA b , RODICA GRECU a , EMIL INDREA c , ELISABETH-JEANNE POPOVICI a ABSTRACT. Nanostructured ZnCdS thin films with variable thickness and high transparency were deposited under variable growth parameters on optical glass platelets, using chemical bath deposition. UV-VIS absorption/reflection spectroscopy, X-ray diffraction, fluorescence spectroscopy, electron microscopy investigations (SEM, EDX) were used to investigate the effect of growth and annealing regime on the films morphology and optical properties. The luminescence properties of copper activated ZnCdS thin films were also investigated. The deposition conditions (medium pH, reagent molar ratio, deposition time) and the presence of the doping ions (copper) influence the morpho-structural properties and optical characteristics of the nanocrystalline zinc-cadmium sulfide thin films. Keywords: thin films; chemical synthesis; optical properties; luminescence INTRODUCTION Zinc sulfide (ZnS), cadmium sulfide (CdS) and their solid solution zinc-cadmium sulfide (Zn1-xCdxS or ZnCdS) are interesting wide band gap semiconductors, which attract much attention because of their interesting optoelectronic properties [1-4]. Due to their special optical and electrical properties, metal chalcogenide thin films have been used in various optoelectronic devices, such as solar energy absorbers, photodetectors and electroluminescent displays [5-7]. Different methods could be used for metal chalcogenide thin films preparation including sputtering [8], MOCVD (metal organic chemical vapor deposition) [9], SILAR (successive ionic layer adsorbtion and reaction) [10], pulsed laser deposition [11], chemical bath deposition (CBD) [12] or electrodeposition [13]. Among them, a Raluca Ripan“ Institute for Research in Chemistry, “Babes-Bolyai” University, 30 Fantanele, 400294, Cluj-Napoca, Romania; marialadar@yahoo.com b Faculty of Chemistry and Chemical Engineering, “Babes-Bolyai” University, 400028 Cluj-Napoca, Romania c National Institute for R & D of Isotopic and Molecular Technology, 71 Donath, 103,400293 Cluj-Napoca, Romania
204 MARIA ŞTEFAN, IOAN BÂLDEA, RODICA GRECU ET ALL CBD is a simple and inexpensive method to produce uniform and adherent films onto a variety of substrates. There are few literature data referring to the chemical bath deposition of ZnCdS thin films with optical properties illustrating that the characteristic films properties strongly depend on chemical bath deposition conditions [14,15]. In order to control the quality of ZnCdS thin films, supplementary studies aiming at the optimization of CBD parameters are needed. The paper presents our results on the growth and characterization of some reproducible ZnCdS thin films prepared by chemical bath deposition. The effect of cadmium ions addition into the chemical deposition bath on the quality of metal chalcogenide thin films is investigated. Moreover, attempts were made to prepare ZnCdS thin films with luminescent properties using a special doping procedure, not mentioned in the literature. RESULTS AND DISCUSSION The preparation of ZnCdS thin films by CBD was based on the reaction, in alkaline medium (NH3), between zinc acetate, Zn(CH3COO)2 and cadmium acetate, Cd(CH3COO)2 as metal sources and thiourea (NH2)2CS, as chalcogen source. The main chemical process for zinc-cadmium sulphide thin films formation is described by the following equation: M (CH3COO)2 + (NH2) 2 CS + 2OH - → MS + H2CN2 + 2H2O + 2CH3COO - where M=Zn and Cd The formation of thin films takes place either in the bulk of the solution due to the spontaneous precipitation of ZnS and CdS (homogeneous reaction) or at the surfaces of the substrate leading to the film formation (by heterogeneous reaction). Our previously studies on chemical bath deposited ZnS thin films [16] pointed out the importance of sodium citrate [Cyt] as complexing agent. Based on our results, the standard chemical deposition bath corresponds to the following reagent ratio: [Zn 2+ ]: [Cyt 3- ]: [NH3]: [thiourea] =1:3:20:10. Starting from this bath, ZnCdS /glass/ ZnCdS hetero-structures were prepared by replacing 5 ÷100 mol % of zinc acetate with cadmium acetate. Zinc-cadmium sulfide thin films were grown by multilayer technique. Four consecutive layers were deposited on glass platelets to give ZnCdS /glass/ ZnCdS heterostructures. For the same deposition time, addition of cadmium acetate into the standard chemical bath used for ZnS-film deposition does not deteriorate the film quality. The as obtained ZnCdS thin films possess good adherence to the substrate, are transparent and show colors varying from white-yellowish to orange-yellowish, depending on the Cd 2+ - amount from the chemical deposition bath.
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R /(mol m -2 s -1 ) 0.06 0.05 0.04
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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6 PROFESSOR IOAN BÂLDEA AT HIS 70
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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STUDIES ON WO3 THIN FILMS PREPARED
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PREPARATION AND CHARACTERIZATION OF
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STUDY OF THE CHROMATOGRAPHIC RETENT
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LOWER RIM SILYL SUBSTITUTED CALIX[8
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IRON DOPED CARBON AEROGEL AS CATALY
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CONCLUSIONS 148 CRISTINA MIHALI, GA
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