Abstract
Cadmium sulphide (CdS) thin films were deposited on glass substrates by the chemical bath deposition (CBD) method, using anhydrous cadmium chloride (CdCl2) and thiourea (CS(NH2)2) as sources of cadmium and sulphur ions respectively. The influence of bath temperature (Tb), deposition time (td) aSnd [S]/[Cd] ratio in the solution on the structural, morphological, chemical composition and optical properties of these films were investigated. XRD studies revealed that all the deposited films were polycrystalline with hexagonal structure and exhibited (002) preferential orientation. The films deposited under optimum conditions (Tb = 75?C, td = 60 min and [S]/[Cd] ratio = 2.5) were relatively well crystallized. These films showed large final thickness and their surface morphologies were composed of small grains with an approximate size of 20 to 30 nm and grains grouped together to form large clusters. EDAX analysis revealed that these films were nonstoichiometric with a slight sulphur deficiency. These films exhibited also a transmittance value about 80% in the visible and infra red range.
Highlights
Amongst of the chalcogenide thin films like PbS, Cadmium sulphide (CdS), ZnS and MnS, CdS appear as an interesting material for using as n-type window layer for p-CdTe and chalcopyritebased solar cells such as p-CuInSe2, and/or p-Cu(In,Ga)Se2 (CIGS) [1]
The intensity of the (002) plane is found to be increased when increasing bath temperature up to 75 ̊C, which decreased afterwards. This suggests that the crystallinity of these films increases when the bath temperature increases; which is explained by the increase in films thickness due to decomposition of reactants and production of ions which is necessary for films formation
The decrease of the (002) plane intensity for films deposited at bath temperature greater than 75 ̊C indicates a deterioration of the crystallinity which is attributed to the relatively lower thicknesses of the films resulted (Figure 2)
Summary
Amongst of the chalcogenide thin films like PbS, CdS, ZnS and MnS, CdS appear as an interesting material for using as n-type window layer for p-CdTe and chalcopyritebased solar cells such as p-CuInSe2, and/or p-Cu(In,Ga)Se2 (CIGS) [1] This is because CdS has high transparency, wide and direct band gap transition (2.42 eV), photoconductivity, high electron affinity and n-type conductivity. [6], molecular beam epitaxy (MBE) [7], metal organic vapour phase epitaxy (MOVPE) [8], successive ionic layer adsorption and reaction (SILAR) [9], and physical vapour deposition (PVD) [10] Among these methods, the CBD technique is relatively simple, low cost compared to other methods requiring vacuum environment and its capable to yield films with good quality at optimum growth conditions. The aim of this present work is to study the influence of some deposition parameters, such as bath temperature, deposition time and [S]/[Cd] ratio in the solution (thiourea to cadmium chloride concentration) on the crystalline structure, surface morphology, chemical composition and optical properties of CdS thin films prepared by JMP
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