Investigating the Optical Properties of Zinc Sulphide Thin Films Deposited from Chemical Acidic Baths
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Date
2012-06-14
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Abstract
A well adherent thin film of zinc sulphide (ZnS) has been deposited on silica glass substrates
from acidic baths containing zinc chloride, thioacetamide and urea. Films of different thickness
(684nm, 572nm, 523nm, and 271nm) were obtained. SEM micrograph of the as-deposited ZnS
thin film, show the film to be uniform, dense, homogenous, and composed of largely irregular
shaped grains of diameter in the range of 300 – 500 nm. These large grains are comprised of
smaller spherical grains of 100 – 200 nm diameter. EDAX results are consistent with the
formation of thin films of ZnS deposited on silica glass substrates. A UV mini Schimazu UV –
VIS Spectrophotometer was used to determine the optical absorbance of the films as a function
of wavelength at room temperature over the wavelength range 200 – 800 nm. The samples were
then thermally annealed for one hour, at temperatures of 300°C, 400°C and 500°C, after which
the absorbance of the films were again recorded. The absorbance of the films decreased with
increasing annealing temperatures indicating an increase in transmittance with increasing
annealing temperatures. The band gap values obtained varied between 3.64 eV and 3.97 eV, for
as deposited films and increased between 3.98 eV and 4.00 eV after annealing. The increase in
band gap with annealing temperature might be attributed to the improvement in crystallinity in
the films. The high transmittance of the films together with their large band gap makes them
good materials for application as a window layer for solar cells.
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) , APRIL, 2012