الفهرس 
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Abstract
The present thesis is devoted to study the structural properties, DC conductivity, AC conductivity and optical properties of TlInSe2 as well as current – voltage and capacitance – voltage characteristics of Ag/p-TlInSe2/Ag.
The structural properties were examined using X-ray diffraction technique. TlInSe2 at room temperature was found to be tetragonal system with lattice parameters of a = 8.063 Å and c = 6.827 Å. The structural parameters, such as crystallite size D, micro strain ε and dislocation density δ were calculated.
DC electrical conductivity (σ_dc) of TlInSe2 single crystal showed a semiconductor like behavior. AC conductivity of the TlInSe2 in pellet form obtained from single crystal was found to obey the power law, i.e. σ_ac (ω)= Aω^s, and dominated by the correlated barrier hopping (CBH) model. The obtained activation energy values of the AC conductivity have confirmed that the hopping conduction is the dominant one. Where, a decrease in these values has been noticed with the increase in frequency. The density of localized states N(E_F) close to Fermi level for TlInSe2 was obtained for the investigated temperature and frequency range. Both dielectric constant (ε_1) and dielectric loss (ε_2) decrease with increasing frequency while they increase with increasing temperature. The frequencies corresponding to maxima of the imaginary electric modulus at different temperatures were used to calculate the relaxation time. A decrease in the relaxation time τ was observed with the increase in temperature. The average hopping distance R and the average time of charge carrier hopping between localized states t were determine for the investigated range of frequency and the value of the maximum barrier height W_M was calculated as well. The dielectric relaxation mechanism was also explained by the Cole–Cole types.
The optical properties of flash evaporated TlInSe2 thin film have been characterized by using spectrophotometric method in the spectral range of 200 – 2500 nm to determine the absorption spectral behavior as well as the optical gap. The transmittance and reflectance measurements for the as-deposited TlInSe2 thin film showed that an absorbing for light waves 200 – 1000 nm while the film is optically transparent in range 1000 – 2500 nm.
The temperature dependence of the current – voltage characteristics of theAg/p-TlInSe2/Ag device allowed the calculation of the barrier height and ideality factor. The capacitance value of the device as a varactor revealed a constant value over the reverse bias voltage. Study of the frequency and temperature range at which the varactor is sensitive was achieved. The device capacitance dependence on the frequency initiates with a maximum value at certain frequency, after this critical value the device capacitance decreases with increasing frequency, until reaches to saturate at nearly constant value for all the investigated temperature range. The device capacitance increases with increasing temperature for all the investigated frequency range. The temperature coefficient of capacitance (TCC) revealed a very small change in capacitance over specified temperature range. Hence, the Ag/p-TlInSe2/Ag device represents a varactor type and can be used for Radio Frequency (RF) wave detection.