الفهرس 
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Abstract
This thesis is the first study of ZnGa2Te4 properties which is one of the defect chalcopyrite or the ordered vacancy compounds. Thin films of ZnGa2Te4 have been deposited by thermal evaporation technique on glass, pyrographite and silicon substrates whose temperature was held at room temperature. The structural, optical, electrical and switching properties of ZnGa2Te4 thin films have been studied. p-ZnGa2Te4/n-Si HJD has been fabricated. Also, the analysis of current-voltage, capacitance-voltage and impedance spectroscopy of this diode has been performed.
The presence of impurities and their percentage in the investigated compound was checked using (EDX). (DTA) thermogram depicts the glass transition and the crystallization temperature .The structural properties of ZnGa2Te4 in both powder and thin film forms have been investigated using (XRD). The analysis of the powder pattern confirms the polycrystalline nature with tetragonal structure. The as-deposited films as well as those annealed at annealing temperature, are amorphous in nature, while, those annealed at showed a polycrystalline structure. Both (TEM) and (AFM) analyses support the nanostructure of ZnGa2Te4.
The optical properties of the as-deposited ZnGa2Te4 thin films have been investigated. The transmittance T and reflectance R of the films were measured in the spectral range from 500 to 2500 nm. The optical constants n and k have been computed using Murmann’s exact equations. The obtained data of the refractive index n was described by the Wemple–DiDomenico single oscillator model. Analysis of the obtained values of the refractive index yielded the oscillator parameters ( , ) and the static refractive index . Analysis of the optical absorption coefficient revealed an in-direct optical transition for the as-deposited films. The values of optical energy gap were determined. Finally, the dependence of the real and imaginary parts ( , ) of the optical dielectric constant, the relaxation time , the dissipation factor and the optical conductivity on the photon energy were studied.
The dc conductivity for ZnGa2Te4 thin films of thicknesses range 80-601nm were measured in the temperatures range 303-423K. The obtained results showed the semiconductor behavior for these films. The conduction activation energy has one value for each thickness indicating the presence of one conduction mechanism through the studied range of temperatures, which can be interpreted according to Mott and Davis model.
The switching phenomenon for ZnGa2Te4 thin film of thickness 601nm, as a representative example, was measured in the temperature range 293-373K. Both dynamic and static I-V characteristics curves are typical for a memory switch devices. Both the mean value of the threshold voltage and the threshold electrical field decreased exponentially with increasing temperature. The values of switching activation energy ∆Eth and the threshold resistance activation energy ΔER are calculated. The data obtained for the switching characteristics were interpreted by thermal model based on the high values of and the ratio of which is found to be greater than 0.5.
Hot probe test indicated that ZnGa2Te4 is p-type semiconductor. P-ZnGa2Te4/n-Si HJD has been fabricated. The dark current-voltage characteristics of this HJD have been studied in the temperature range 303-423K. These characteristics showed a rectification behavior. At the lower voltages, , the electrical charge transport controlled by thermionic emission theory (TE). At the higher voltages , there are three conduction mechanisms, the space charge-limited current (SCLC) , trap-charge limited current (TCLC) and trap free space charge-limited current . The device showed a non-ideal diode due to the large values of the parameter ni (ni > 1). Analysis of the reverse current shows that is limited by the carrier generation-recombination process and thermally activated with activation energy .
The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the p-ZnGa2Te4/n-Si HJD were measured at variable frequency range 5 - 500 kHz and in the temperatures range 303K-423 K for all measurements. The values of interface states density were calculated. The related parameters such as the built-in potential and the doping concentration values were extracted. The series resistance-voltage characteristics of this diode were measured. The corrected capacitance and corrected conductance were calculated. The and characteristics of this diode were studied. The dielectric properties and ac conductivity of this diode were measured. Finally, the dielectric constant-voltage ( -V), dielectric loss-voltage ( -V), the loss tangent-voltage and the ac conductivity-voltage characteristics of this diode were studied.
The impedance spectroscopy of the p-ZnGa2Te4/n-Si HID has been studied at a wide range of temperature 297-473K and in a frequency range 42Hz–5MHz. The complex impedance analysis suggested non-Debye (polydispersive) type electrical relaxation. The bulk resistance as well as the bulk capacitance increased with increasing temperature.The electrical and dielectric properties of this diode were studied using ac impedance spectroscopy technique in the considered frequency and temperature ranges. The dc conductivity showed a typical Arrhenius behaviour. The obtained results of dc conductivity were interpreted by Mott and Davis model due to electron hopping in the localized states of the band tail. Temperature dependence of the calculated total electrical conductivity and ac conductivity were studied for this diode in the studied frequency and temperature ranges. The ac conductivity mechanism was found to obey Jonscher’s universal power law .The values of frequency exponent s decreased with increasing temperature, therefore, the temperature dependence of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping (CBH) model. The electrical activation energy values decreased with increasing frequency. The dielectric constant and dielectric loss decreased with increasing frequency and increased with increasing temperature. The dielectric analysis results confirmed a non-Debye type dielectric relaxation mechanism of this diode.