Chemical-bath deposition

Chemical bath deposition is a technique in which thin semiconductor films are deposited on substrates immersed in dilute solutions containing metal ions and a source of hydroxide, telluride, sulfide, selenide, etc., ions. One of the first chemically deposited semiconductors, reported in 1869, was a PbS thin film [26]. During the ensuing 140 years, CBD has been used to deposit films of metal sulfides, selenides, and oxides, and various other compounds. While it is a well-known technique in a few specific areas (notably photoconductive lead salt detectors, photoelectrodes, and, more recently, thin-film solar cells), it is by and large an under-appreciated technique. 

The more recent interest in all things nano has provided a boost for CBD, since it is a low-temperature, solution-phase (almost always aqueous) technique, which often results in very small crystal sizes. This is evidenced by the existence of size quantization commonly found in CBD semiconductor films. The intention of this review is to provide an overview of how the technique has been used to fabricate nanocrystaUine semiconductor films, as well as some of the properties of these 

The solubihty product (IQ is the key parameter for understanding the basic aspects of CBD of thin-film semiconductors [12, 23]. The solubility product of a material is defined as the product of the concentrations of the ions of this material dissolved in a given electrolyte. In general the dissolution of an A By material is expressed according to 

This indicates that fQ increases with the solubility of the salt We may keep in mind that JC is a thermodynamic parameter derived from the free energies of formation (AG°) of the species involved in the dissolution of the solid compound A By(s) into its ions in solution (xA (aq) and yB (aq)) at thermodynamic equilibrium according to 

As a thermodynamic parameter, will indicate the range of ion concentrations in which the compound precipitates. This serves to define what concentrations of ions are required in the deposition electrolyte to ensure (or avoid) compound precipitation. For example, for CdTe the Ks value is 10 , and therefore 

Consideration of the chemistry that implements non-electrochemical solution growth processes along with related mechanistic aspects may be useful to enhance the understanding of electrochemical deposition in similar baths. The chemical deposition of CdS has been chosen as a model for this discussion by reason of the wealth of related publications and the advanced level of knowledge existing for this system (e.g., [45]). 

Within the scope of applications in electronics, electrooptics, and photovoltaics, several metal sulfides and selenides, mostly binaries such as CdS, CdSe, Bi2S3, Bi2Sc3, PbS, PbSe, Ag2S, TlSe, M0S2, ZnSe, ZnS, and SnS2, but also the ternaries 

To be specific, let us consider the global reaction between dissolved cadmium ions and thiourea molecules in ammonia solutions, which can be represented as 

The commonly accepted underlying mechanism involves decomposition (hydrolysis) of thiourea in the alkaline solution to form sulfide ions (3.10), which react with Cd ions released by the decomplexation reaction (3.11), with precipitation of cadmium sulfide (3.12) upon exceeding the solubility product of the compound 

The aqueous decomposition of thiourea to sulfide and cyanamide has been found to be catalyzed by metal hydroxide species and colloidal metal hydroxide precipitates. Kitaev suggested that Cd(OH)2 is actually required for CdS film formation to occur by adsorption of thiourea on the metal hydroxide particles, followed by decomposition of the Cd(OH)2-thiourea complex to CdS. Kaur et al. [241] found 

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GIAB studies of sputtered thin films of different composition for tribological applications have been reported [4.157-4.159]. The technique has been used to study the structure of very thin GdS layers (deposited by chemical bath deposition) for photovoltaic applications in combination with 6-26 diffraction it enabled identification of their polytype structure [4.160]. Glancing angle diffraction in the GIAB geometry... 

In the following, selected results will be presented on the conventional electrochemical synthesis of metal chalcogenide binary and ternary systems, conducted by employing variants of the methods outlined in the previous sections. A brief account of chemical bath deposition principles exemplified will be addressed at the end of this chapter, as being closely related to electrochemical deposition of thin films. 

The chemical bath deposition of polycrystalline, zinc blende HgSe thin films on TO glass from aqueous alkaline medium has been reported [120]. Examples of electrodeposited ternary mercury compounds will be discussed in the next section. 

Lead sulfide films have been prepared by various deposition processes like vacuum evaporation and chemical bath deposition. Electrochemical preparation techniques have been used in a few instances. Pourbaix diagrams for all three aqueous lead-chalcogen Pb-S, Pb-Se, and Pb-Te systems, along with experimental results and cited discussion on the chemical etching and electrolytic polishing of lead chalcogenide crystals and films, have been presented by Robozerov et al. [201]. 

Pavaskar NR, Menezes CA, Sinha APB (1977) Photoconductive CdS films by a chemical bath deposition process. J Electrochem Soc 124 743-748... 

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

Ortega-Borges R, Lincot D (1993) Mechanism of chemical bath deposition of cadmium sulfide thin films in the ammonia-thiourea system. J Electrochem Soc 140 3464-3473... 

Cachet H, Esaaidi H, Froment M, Maurin G (1995) Chemical bath deposition of CdSe layers from Cd(II)-selenosulfite solutions. J Electroanal Chem 396 175-182... 

Dona JM, Herrero J (1994) Process and film characterization of chemical-bath-deposited ZnS thin films. J Electrochem Soc 141 205-210... 

Niitsoo O, Sarkar SK, Pejoux C, Riihle S, Cahen D, Hodes G (2006) Chemical bath deposited CdS/CdSe-sensitized porous HO2 solar ceUs. J Photoch Photobio A 181 306-313... 

Meth, J. S. Zane, S. G. Sharp, K. G. Agrawal, S. 2003. Patterned thin film transistors incorporating chemical bath deposited cadmium sulfide as the active layer. Thin Solid Films. 444 227-234. 

Chemical Bath Deposition, Electrodeposition, and Electroless Deposition of Semiconductors, Superconductors, and Oxide Materials... 

Kylner, A. Lindgren, J. Stolt, L. 1996. Impurities in chemical bath deposited CdS films for Cu(In,Ga)Se2 solar cells and their stability. J. Electrochem. Soc. 143 2662-2669. 

Arias-Carbajal Readigos, A. Garcia, V. M. Gomezdaza, O. Campos, J. Nair, M. T. S. Nair, R K. 2000. Substrate spacing and thin-film yield in chemical bath deposition of semiconductor thin films. Semicond. Sci. Technol. 15 ... 

O Brien, R McAleese, J. 1998. Deposition and characterization of cadmium sulfide thin films by chemical bath deposition. /. Mater. Chem. 8 2309-2314. 

Mikami, R. Miyazaki, H. Abe, T. Yamada, A. Konagai, M. 2003. Chemical bath deposited (CBD)-ZnO buffer layer for CIGS solar cells. Edited by Kurokawa, K. Kazmerski, L. L. McNelis, B. Yamaguchi, M. Wronski, C. Sinke, W. C. Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (IEEE Cat. No. 03CH37497). PI Vol. 1. pp. 519-522. 

Ennaoui, A. Weber, M. Saad, M. Harneit, W. Lux-Steiner, M. Ch. Karg, F. 2000. Chemical bath deposited Zn(Se,OH)x on Cu(In,Ga)(S,Se)2 for high efficiency thin film solar cells Growth kinetics, electronic properties, device performance and loss analysis. Thin Solid Films 361-362 450 153. 

Yamaguchi, T. Yamamoto, Y. Tanaka, T. Yoshida, A. 1999. Preparation and characterization of (Cd,Zn)S thin films by chemical bath deposition for photovoltaic devices. Thin Solid Films 343-344 516-519. 

Rajebnhonsale, M. R. Pawar, S. H. 1982. Growth and structural properties of Cdi xZnxS films formed by chemical bath deposition technique. Indian J. Pure and Appl. Phys. 20(8) 652-653. 

Lokhande, C. D. Ennaoui, A. Patil, P. S. Giersig, M. Muller, M. Diesner, K. Tributsch, H. 1998. Process and characterisation of chemical bath deposited manganese sulphide (MnS) thin films. Thin Solid Films 330 70-75. 

Gumus, C. Ulutas, C. Esen, R. Ozkendir, O. M. Ufuktepe, Y. 2005. Preparation and characterization of crystalline MnS thin films by chemical bath deposition. Thin Solid Films 492 1-5. 

Valyomana, A. G. Sajeev, T. P. 1991. Photoconductivity studies of CuInSe2 thin films prepared by the chemical bath deposition technique. Physica Status Solidi A 127 K113-K116. 

Zeenath, N. A. Pillai, P. K. V. Bindu, K. Lakshmy, M. Vijakakumar, K. P. 2000. Study of trap levels by electrical techniques in p-type CuInSe2 thin films prepared using chemical bath deposition. J. Mater. Sci. 35 2619-2624. 

Ganchev, M. Stratieva, N. Tzvetkova, E. Gadjov, I. 2003. Kinetics of the chemical bath deposition of ZnSe films. /. Mater. Sci. Materials in Electronics 14 847-848. 

Bindu, K. Lakshmi, M. Bini, S. Sudha Kartha, C. Vijayakumar, K. P. Abe, T. Kashiwaba, Y. 2002. Amorphous selenium thin films prepared using chemical bath deposition Optimization of the deposition process and characterization. Semicond. Sci. Technol. 17 270-274. 

Lokhande, C. D. Pathan, H. M. Giersig, M. Tributsch, H. 2002. Preparation of Znx(0,S)y thin films using modified chemical bath deposition method. Appl. Surf. Sci. 187 101-107. 

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