الفهرس 
Introduction and General SurveyOnly 14 pages are availabe for public view
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Abstract
A systematic investigation of the structural, optical and electrical properties of Se52In48-xPbx
compositions (where x = 28,
31, 36 and 40 at.%) were carried out.
The bulk materials of Se52In48-xPbx were prepared by the fusion and cooling technique. Thin films
of Se52In48-xPbx were deposited under vacuum (10-5 Torr) on glass substrates by thermal
evaporation technique of the bulk compositions.
Results of x-ray diffraction for the powder compositions and thin films were reported and
discussed. There is only one x-ray standard card for In0.03Pb0.97Se number 01- 089 - 3921, which is
available for us and was used for structural identification of the experimentally prepared powder
and films.
The analysis of the x-ray diffraction patterns for the prepared powder of Se52In48-xPbx (where x =
28, 31, 36 and 40 at.%) show that the dominant crystalline phase are hexagonal InSe and cubic
In0.03Pb0.97Se structure. The x-ray diffraction patterns of as deposited and annealed
films were found to be in polycrystalline
state.The optical transmission and reflection spectrum of these films
were measured in the range 1000 - 2200 nm and the optical
constants (absorption coefficient α, refractive index n, extinction
coefficient k, real
r and imaginary part
i of the dielectric
constant) were calculated for Se52 In48-x Pbx compositions films as a
function of photon energy. The absorption data revealed the
existence of allowed direct and indirect transitions. It has been
found that the optical band gap decreases with increasing Pb
content up to x = 36 at.% then, increases as Pb content raised up to
40 at.%.
The results were interpreted in terms of the change in the
average bond energy of the films as a function of composition. The
increase of the optical energy gap at x = 40 at.% could be
attributed to the decrease in the grain size, the reduction in disorder
and decrease in density of localized states in the band gap.
On the other hand, the values of direct and indirect optical
energy gap of Se52In48-xPbx films was found to be increased with
increasing the annealing temperature (90, 165 and 300 °C for one
hour) and it was analyzed on the basis of the theory proposed by
Mott and Davais. But for high percentage of Pb (x = 40 at.%) the
optical energy decreases with annealing temperature (300 °C) and
this is due to the production of surface dangling bond around the
crystallites during the process of crystallization.The temperature dependence of dc conductivity for the as
deposited films of Se52 In48-xPbx in the temperature range (303 –
423 K) was measured. For these films, it is suggested that the
conduction is due to thermally activated process through the
extended states. The effect of composition on the pre-exponential
factor
o and the activation energy E were studied. It is found that
the values of
o and E decreases with increasing Pb content (x =
28, 31, and 36 at.%) but for higher concentration of Pb (x = 40
at.%)
o and E were increased.
Frequency and temperature dependencies of the ac
conductivity ac of Se52 In48-xPbxwere studied. It is found that
ac() increases linearly with increasing frequency and the
absolute temperatures.
The values of the ac activation energy E() decreases with
increasing frequency. This decrease may be attributed to the
increase of the applied field frequency which enhances the
electronic jump between the localized states. In addition it has
been found that the activation energy of the dc conductivity is
higher than that of ac, because of the existence of the electric field
related to energy frequency affected on the charge carriers mobility
as well as decreasing the ac activation energy. The values of the
activation energy E decreases with increasing the Pb content up
to 36 at.%. But for x = 40 at.% the value of E increases. This is
confirmed with the results of optical energy gap (Eg) and dc activation energy (E). The dielectric constant was found to
decrease with increasing frequency. The decrease of for the
films with increasing frequency can be attributed to the
contribution of many components of polarization, ionic, dipolar or
orientation and space charge. On the other hand the dielectric
constant was found to increase as the temperature increases over
the whole investigated range of frequency. This is attributed to the
fact that dipoles in polar materials cannot orient themselves at low
temperature. When the temperature is increased the orientation of
dipoles is facilitated and thus increases the orientational
polarization and in turn increases . The dielectric loss was
calculated and it is observed that decreases with increasing
frequency due to the migration of ions in the material at low
frequencies, and ion vibrations at high frequencies. On the other
hand increases with increasing temperature, which can be
attributed to the fact that orientational polarization is associated
with the thermal motion of molecules leading to the increase of