Effect of Thickness and Temperature Variations on Some Structural, Optical and Electrical Properties of Electron Beam Deposited CdS Thin Films
Keywords:
II-VI thin films, CdS, electron beam deposition, activation energy, absorption coefficien, optical spectra, optical bandgap, electrical propertiesAbstract
Thin films of cadmium sulfide (CdS) by electron beam deposition on glass substrate. The structure of the films was investigated by X-ray diffraction (XRD). The CdS films were found to be crystalline and hexagonal with the c-axis perpendicular to the substrate. Annealing in air at 4000C greatly improved the crystallinity of the films as well as increasing their grain size. The optical properties of the films have been studied by transmission/reflection spectroscopy. The CdS films had optical bandgaps in the range 2.35-2.42 eV, which were dependent on the film thickness as well as on temperature. A reduction in the bandgap was also noticed for the annealed films. In addition, the single-effective oscillator parameters have been evaluated and their dependence upon film thickness discussed.
From d.c. electrical conductivity measurements it was found that the conductivity of the CdS films is a function of the thickness of the film, increasing with the thicker films. The electrical conductivity is greatly improved when the film is air-annealed. From values of the activation energy of conduction it was concluded that conduction is dominated by states close to the conduction band.
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