الفهرس 
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Abstract
Positron Annihilation Lifetime Spectroscopy (PALS) has been used to understand the nature and the possible influence on material performance of specific defects. The positron lifetime results on Zn-doped CdTe showed a vacancy defect with a lifetime of ~ 330 ps. The temperature dependence of the mean lifetime shows that trapping to weak binding energy defects, with positron states similar to the bulk, onsets at low temperatures.
Complex impedance spectroscopy (CIS) technique has been carried out to analyse the electrical transport properties of Zn-CdTe and Si-GaAs single crystals. The Nyquist impedance spectra of the specimens were performed using Gamry G750 potentiostat /galvanostat instrument operating with EIS300 software. The measurements were performed in the frequency range of 100 Hz to 1 MHz at different temperatures. The behaviour of the complex impedance (Z’and Z’’) parameters, D.C. conductivity and the Ac conductivity with frequency and temperature were explained on the basis of the correlated barrier hopping (CBH) and tunneling effect for conduction mechanism. The behavior of the frequency component revels that the conduction mechanism in the frequency range (200:8K) Hz is correlated barrier hopping and the binding distances were deduced.
Therefore the PAL results indicated the sensitivity of the positron lifetime to study the changes in density and size of defects, which in turn can be one of the reasons for changing electrical properties of Zn-CdTe and Si-GaAs single crystals.