الفهرس 
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Abstract
The melt quenched chalcogenide glasses are semiconductors which are useful in several potential applications like memory devices and the reverse phase change optical recording memories. The technological applications of semiconducting materials requires independent control of electrical properties and the optical band gaps , for amorphous materials this is normally achieved in two steps:(a) Conduction in the high density of localized states in the gap, and (b) The introduction of additives in their non-optimal configuration. The melt quenched chalcogenide glasses Ge20BixSe80-x under investigation in this thesis exhibit a p-to-n carrier-type reversal (CTR) which is the striking feature of this system. Structure, electrical properties, and thermoelectric power were studied to illustrate the behaviour of such system. The Key results of this work are summarized as follows: High resolution transmission electron diffraction indicates the structure of Ge20BixSe80-x is amorphous. Transmission pattern show homogeneous structure. Transmission and reflection spectra in the range from 300 to 2500 nm were studied to elucidate optical properties of Ge20BixSe80-x. Optical gap decrease with increasing thickness and it decreases with increasing Bi. The extinction coefficient, refractive index, absorption coefficient and other optical parameters were studied. Measurements of thermoelectric power as function of temperature to determine seebeck coefficient, thermoelectric efficiency and figure of merit. The effect of increasing Bi addition was to change the conduction type from p- type to n- type.Bi dopant has striking effect on electrical conductivity. For Bi= 5% at wt. and Bi= 15 at wt. has semiconductor trend since conductivity increases as temperature increases while for Bi= 10% at wt. conductivity shows degeneracy as 𝜎 decreases with increasing temperature.High temperature ac conductivity, ac capacitance, and ac dielectric constant was investigated for the alloys in a wide range of frequency for temperatures from 300C up to 1000C. The effect of frequency on p- to n- type transition was investigated for all compositions.A test of the ferroelectric hysteresis loop for the thin film alloys under investigation was made to insure the applicable concentrations.