Investigating the Optical properties of cd1-xznxs thin films deposited by the Dip Technique
Loading...
Date
2010-07-18
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Thin films of Cd1-xZnxS ternary alloy have been prepared by the dip technique using thiourea and the nitrates of cadmium and zinc. The optical properties have been investigated by spectrophotometry and photoconductivity studies. The calculated film thickness using the gravimetric method were 18.85μm, 8.61μm, 5.06μm, 6.23μm for x= 0.2, 0.4, 0.6, 0.8 respectively. The absorption spectra, A(λ), of the films at normal incidence of light were obtained in the spectral region 300–900 nm using LKB ultrospecII 4050 UV/Visible spectrophotometer. The optical band gap of the as deposited films varied from 2.42eV (x =0.2) to 3.61eV (x =0.8), that is, the band gap increased with increasing Zn concentration of the alloy. The as deposited samples were thermally annealed in air for about an hour at temperatures of 100°C, 200°C and 300°C and the absorption spectra again recorded. It was revealed that thermal annealing decreased the optical band gap; this may be due to improved crystalline structure of the samples as a result of the heat treatment. The average extinction coefficient for the as deposited samples were 6.89x10-3, 10.27x10-3, 19.93x10-3, 22.16 x 10-3 for x= 0.2, 0.4, 0.6, 0.8 respectively. The films formed were moderately photoconductive in the as deposited state with photocurrent peaking at 98 μA in the Cd0.8Zn0.2S sample. The photocurrent decreased as Zn content increased in the solution. The Cd0.8Zn0.2S film showed a high photoconductivity around 2.20 eV. This energy was quite close but smaller than the corresponding band gap of 2.42 eV of the sample with a difference of 0.22 eV. Transition from localized states within the forbidden gap is speculated to be the cause for the photoconductivity.
Description
A Thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirement for the degree of
Master of Science (Solid State Physics)