Optical Properties of CdZnS Thin Film by CBD Method
Abstract
Using chemical bath deposition (CBD) technique, (Cd-Zn)S:CdCl2 thin films were prepared on glass substrates. Room temperature photoluminescence analysis in the 400-700 nm emission wavelength ranges for the excitation energies 365nm show the ‘well known’ green emission band related to exciton-donor complexes formed in presence of S / excess Cd are observed in the PL emission spectra of various rare earth doped (Cd-Zn)S:CdCl2 films. In doped films, characteristic emissions of lanthanide such as Ce are observed. Some properties related to nanocrystalline effects are also found. The influence of variation of ratio of cadmium and sulphur was studied on the PL emission intensity of (Cd-Zn)S:CdCl2 thin films. In a selected ratio of cadmium and sulphur for which emission intensity was highest, the effect of impurity concentration on PL emission intensity was studied.
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Introduction
Cadmium sulphide is a suitable window layer for solar cells [1-3] and also finds applications as optical filters and multilayer light emitting diodes [2], photo detectors [3], thin film field effect transistors [3-5], gas sensors [6], and transparent conducting semiconductor for optoelectronic devices [7]. Among the various known methods to synthesis CdS thin films; the reliable, simple and cost effective route is one using the chemical bath deposition (CBD) technique.
The wide technological applications of CdS type materials make the PL and PC studies important. Some of the important applications of PL are lamp phosphors and display devices and those of PC are xerography and IR detectors etc. PL edge emission was extensively studied in
CdS by several workers [8-10] and was related to excitonic transitions involving donor/acceptor-exciton complexes [4]. Similarly PC of CdS and CdSe were extensively studied by Bube and co-workers [11, 12]. The effect of alloying of CdS, CdSe and other II-VI group compounds on the PL and PC properties has attracted the interest of research workers in recent years. The rare earth ions are well known to form efficient luminescent centers as they show distinct absorption and emission transitions within the 4fN shell configuration [13,14]. Mixed base (Cd-Zn)S has a wider band gap than CdS, which makes it suitable for Phospho-Luminescent screen pigment manufacture etc.[15]. Thus in the present paper (Cd-Zn)S is used as base material. Further rare earth material cerium has been used as impurity as they form prospective luminescent material. CdCl2 has been used as flux which facilitates the incorporation of the rare earth ions into the lattice and also helps in recrystallisation of (Cd-Zn)S [16]. The present work concerns with PL studies of (Cd-Zn)S:CdCl2,Ce films prepared at different preparative condition
Conclusion
An intense PL emission spectra obtained for the nanocrystalline structured (Cd-Zn)S:CdCl2,Ce films. Films were prepared at different concentration of contents and preparative conditions and it has observed that the PL intensity peak observed for the sample (Cd.8-Zn.2)1S.9:CdCl2,Ce prepared at 60°C for 1.25 hour for 6ml rare earth impurity. Shift in wavelength for emission peak also observed indicating the substitution of impurity in the crystal lattice.