الفهرس 
General IntroductionOnly 14 pages are availabe for public view
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Abstract
It is well known that amorphous chalcogenide materials are considered a group of inorganic glassy materials contains one or more of the chalcogenide elements e.g. S, Se or Te, with more electro-positive elements from the periodic table such as Ge, Ga, Sn, In, Sb, etc. The bonds in chalcogenide glassy materials are generally less robustand more weakly bonded as compared with the oxide glasses.
In the present work, amorphous chalcogenide glassy bulk materials of the ternary compound Ge25-xGexSe75 (where 5.97≤x≤23.95) were prepared in vacuum sealed silica tubes at vacuum pressure of 10-3Pa from high purity elements (99.999 %) of Ge, Ga and Se.Thin films of different thickness of the selected compositions were prepared by thermal evaporation technique via depositing the corresponding powdery sample onto pre-cleaned glass substrates.
The structural characterization of the prepared Ge25-xGexSe75materials in the form of powder and the corresponding thermally evaporated films has been investigated using different techniques.
The amorphous nature of the prepared Ge25-xGexSe75 bulk ingot materials of the selected compositions and the corresponding elemental chemical composition as well as their thermal stability have been investigated using, respectively,X-ray diffraction (XRD),energy dispersive X-ray spectromtery (EDX) and Differential Scanning Calorimetry (DSC) techniques.
Structural characterization of the thermally evaporated Ge25-xGaxSe75 films deposited onto glass substrates and the corresponding chemical composition as well as their surface morphology have been studied. Transmission electron microscope (TEM) and electron diffraction (ED) studies have been also conducted to confirm the structure nature of the deposited films. the effects of the annealing temperature on the deposited films has been performed at different temperatures to identify the temperature degree of the amorphous-to-crystalline phase transition.
The optical properties of the amorphous chalcogenide Ge25-xGaxSe75 thin films ternary compounds deposited onto glass substrates have been studied using the spectrophotometric measurements of the transmission, T(λ) and reflection, R(λ) spectra at normal light incident in the wavelength optical range 250-2500 nm. The refractive index, n and the optical absorption coefficient, of the deposited films have been calculated. The analysis of the refractive index dispersion below the inter-band optical absorption edge has been studied using the well-known single effective oscillator model proposed by Wemple–DiDomenico (WDD), whereby, the oscillator parameters “Eo” and “Ed” were determined. The analysis of the optical absorption coefficient, of the deposited films in the fundamental absorption edge in the wavelngth range 250-780 nm; were performed to evaluate the values of the optical band gap and identify the type of the optical transitions. The effects of the annealing process on the optical properties of the deposited films has been also conducted in such cases of the amorphous and crystalline states.
The DC and AC electrical conductivity of the deposited Ge25-xGaxSe75 films was also performed. The DC conductivity of the investigated films was studied in the temperature range 303-550 K during both of heating and cooling cycles. The temperature-conductivity variation for the heating cycle exhibit two segmentsThe DC and AC electrical conductivity of the deposited Ge25-xGaxSe75 films was also performed. The DC conductivity of the investigated films was studied in the temperature range 303-550 K during both of heating and cooling cycles. The temperature-conductivity variation for the heating cycle exhibit two segments regions, where the activation energy, E for such region was determined for the investigated compositions. While for the cooling cycle, the temperature-conductivity curve showed only one segment region where, the corrsponding activation energy, E was caclulated.
The AC conductivity of the deposited Ge25-xGaxSe75 films was also present in the frequency range 100 Hz-5 MHz. The frequency and temperature dependence of the AC conductivity was found obys the S.R. Elliott power law of the form σac (ω)=Aωμ, where the exponent, for the investigated composition as a function of the exact Ga at % was calculated. The exponent variation with the temperature for the investigated samples was successfully disscussed in terms of the correlated barrier hopping theoretical model. Furthermore, the frequency and temperature dependence of the dielectric constant ε∖ and loss tangent, tan , were also presented.