الفهرس 
Theoretical Background and Literature ReviewOnly 14 pages are availabe for public view
 |  | from | 109 |  |  |
| | | from | 109 | | |
Abstract
The growth of crystalline material has become an important part of technical activity in recent years, so the aim of the thesis is to obtain the ternary compound single crystal (TlInSe2) and study its various physical properties in order to reach the possibilities of application, which in turn depend on the constants and physical behavior of this Compound.
The structure of TlInSe2 in powder form was examined using X-ray diffraction. TlInSe2 at room temperature was found to be tetragonal system with lattice parameters of a = 8.063Å and c = 6.827Å. The structural parameters, such as crystallite size D, micro strain ε and dislocation density δ were determined from XRD spectra.
The DC Electrical conductivity of TlInSe2 has been evaluated in the temperature range from 298 to 423 K. and the value of activation energy was deduced to be 0.43 eV with energy gap 0.86 eV.
The dependence of AC conductivity and dielectric properties on the frequency and temperature for TlInSe2 in pellet form obtained from TlInSe2 single crystal were studied in the frequency range of 42 Hz – 5 MHz and temperature range of 294 – 393 K. The AC conductivity of the TlInSe2 was found to obey the power law, i.e.σ_ac (ω)= Aω^s. AC conductivity of TlInSe2 was 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 in the range of 1.02 – 2.8 ×1019 eV-1 cm-3 for various temperatures and frequency. The frequencies corresponding to maxima of the imaginary electric modulus at different temperatures were found to satisfy an Arrhenius law with activation energy ER of 0.32 eV. 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 found in the range of 6.10 – 11.95 nm and 2×10-7 – 2.4×10-2 s respectively, for the investigated range of frequency and the value of the binding energy WM was 0.52 eV. The dielectric relaxation mechanism was also explained by the Cole-Cole types.
The transmittance (T) and the reflectance (R) of TlInSe2 were determined at normal incidence in the wavelength range 200 - 2500 nm by means of a double beam spectrometer. The value of absorption coefficient α was computed by special computer program. The optical band gap E_g was determined to be 0.84 eV with allowed direct transition.
Current density – Voltage characteristics of Ag/p-TlInSe2/Ag of Schottky diode were recorded as a function of temperature. At sufficiently low voltages in the Schottky barrier region, the data of the forward bias I–V characteristics measurement were analyzed. The common analysis of the curve in this region is based on thermionic emission theory, and then some factors were calculated as the barrier height Φ_b ≈ 0.98 eV and ideality factor n ≈ 8.25 at room temperature.
The capacitance – dc voltage characteristics of TlInSe2 diodes have been recorded at room temperature and study the behavior by increasing temperature.
Capacitance - frequency (C-F) characteristics was studied at different temperature in the range of 303 - 383 K, 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 saturation is reached at nearly constant value for all the investigated temperature range.
Capacitance – temperature (C-T) characteristics were studied at different frequencies in the range of 1 – 10 KHz, 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.