الفهرس 
General IntroductionOnly 14 pages are availabe for public view
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Abstract
Tin sulfide (SnS) bulk ingot material was prepared by direct fusion
of the stoichiometric proportions of the constituent elements in vacuum
sealed silica tube, following controlled heating and cooling stages. The
X-ray powder diffraction pattern indicated that the prepared powder
sample belongs to SnS orthorhombic structure. The corresponding lattice
parameters are a =0.43196, b=1.11850, and c=0.39746 nm.
SnS thin films with different thickness (155, 225, 283, 470 and 585
nm) were prepared by conventional thermal evaporation technique in
vacuum pressure of 10-3 Pa, onto glass substrates held at room
temperature.
The X-ray and electron diffraction study indicates that the asdeposited
SnS films of thickness greater than 283 nm are partially
crystalline with very small scattering volume. The crystalline nature of
the as-deposited thinner SnS films (of thickness ~100 nm) was also
confirmed using transmission electron microscope and the corresponding
electron diffraction patterns. It was also observed from the X-ray
diffraction that when the deposited SnS films being air annealed up to
423 K the observed peaks intensity increases (i.e. increase the
crystalinity); however with further increasing in the annealing
temperature to 473 K the intensity of the observed peaks begins to
decreases. The crystal size increases with increasing the film thickness
and also with the increase of the annealing temperature. The EDX
analysis of the deposited SnS films reveals that, the as-deposited thinner
SnS films as well as thicker films annealed at annealing temperature ≥
473 K are deviated from stoichiometry.
The optical transmission and reflection spectra were recorded for
different film thickness in the wavelength range 350-2500 nm, and the
data was used to calculate the refractive index, absorption coefficient and
optical band gap. It was found that the refractive index of the deposited
SnS films increases as the film thickness increase. The dispersion of the
refractive index data was described according to the Wemple-
DiDomenico single oscillator model whereby, the single-oscillator energy
`gap’ (Eo), dispersion energy (Ed), static refractive index (n (0)), static
dielectric constant, ε
s as well as the other related optical parameters for
the investigated SnS film thicknesses were determined. The refractive
index data was further analyzed for different film thickness using the
known Sellmeier-dispersion relation from which the average oscillator
position o
λ , average oscillator strength o S , and dispersion parameter
( ) s o E S have been calculated. The analysis of the optical absorption
coefficient for the investigated thickness of SnS films reveals the
presence of a direct allowed optical transition. The determined optical
band gap was found to be decreases with increasing the film thickness.
The current-voltage characteristic of SnS indicates ohmic behavior
in the measured voltage range 0-9 V. The film resistance measured at
room temperature shows considerable decrease with the increase in the
film thickness, reach almost constant value for higher film thickness (585
nm which is the best thickness for photovoltaic application). It was also
observed that for all of the investigated film thicknesses, the conductivity
dependence of temperatures showing normal semiconducting behavior
with single linear part within the measured temperature range (300-460
K); indicates one type of conduction mechanisms through thermally
activated process. The determined activation energies values were found
to be decreased with the increase of the film thickness.
The thickness dependence of the film resistivity is analyzed using
the effective mean free path model on the basis of classical size effect.
The analysis leads to the evaluation of the important physical parameters
i.e. effective mean-free-path of the infinitely thick crystalline film and the
bulk resistivity.
The I-V characteristic of SnS/Ag-CdS/ITO photovoltaic solar cell
has been investigated. The obtained result indicates a poorest
photovoltaic behavior, which was attributed in the present work to the
non homogeneous, granular, loosely adherent, and not pinhole free of the
chemically deposited CdS films. These defects beside the mismatch
between SnS (orthorhombic structure) and CdS (cubic structure) cause a
short circuit and/or large leakage current of the device.