الفهرس 
Chapter1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
CdSe1-xTex polycrystalline materials with (x = 0, 0.2, 0.4, 0.6, 0.8 and 1 at. %) were prepared by means of conventional thermal evaporation technique. CdSe1-xTex thin films of about 0.5 µm have been produced.
The X-ray diffraction patterns revealed that the prepared films have good crystallinity. The XRD pattern of the pure CdSe thin films illustrated a preferential oriented peak (002) at 2θ = 25.26o, which is in a good agreement with the standard of CdSe powder for the structure of hexagonal crystal. Likewise, the XRD spectra of pure CdTe thin films shows a strong peak at 2θ = 23.66o, corresponds cubic structure of (111) reflection.
The envelop method has been presented to calculate the refractive index, film thickness, hence other optical parameters.
The value of the refractive index rises with increase of the Te concentration which leads to a decrease in the energy gap.
The dispersion parameters such as the dispersion energy parameter (E_d), zero frequency dielectric constant (ε_0) and the linear refractive index (n_0) increase with increase Te content while E_0 decrease.
Non- linear refractive index n2 was estimated according two models Tichy-Ticha. The two models ensure that the non-linear refractive index decrease with growing wave length and increases with increasing Te concentration. The WDD single oscillator model was used to compute the refractive index dispersion. The linear refractive index and WDD parameters have strong correlations with the nonlinear refractive index of Cd-Se-Te films.
The absorption coefficient could be evaluated in the strong absorption region of the experimentally value of reflection and transmission of the wavelength. For the transitional region between cubic and hexagonal crystal structure; phases are detected, absorption feature represents an average of the two phases.
The optical band gap was calculated using the films’ absorption spectra in the high absorption region (104 cm-1). With a rise in Te concentration, the band gap reduces from 1.677 eV (CdSe) to 1.412 eV for CdSe0.4Te0.6 (x = 0.6), and then it increases to 1.486 eV (pure CdTe) for higher Te concentrations. This reduction in optical band gap could be related with the increase of the restricted states within the band gap by the additional of Te and improved the efficiency of solar cell.
In order to prepare CdTe films that were doped with Cu using an ion exchange approach, thermal evaporation techniques were also utilised. The doped films were heat treated (annealed) in vacuum at a variety of annealing temperatures (RT, 100, 200, 300, 400, and 500 oC), for 30 minute, to facilitate the diffusion of dopant Cu material.
Both film thickness, d and the refractive index, n were calculated using the technique of envelop from transmission.
The refractive index value rises as annealing temperature rises. An increase in refractive index reduces the energy gap and improves the solar cell efficiency.
Scherrer and William-Hall equations remained used to compute the lattice strain and crystallite size. It is practical that the lattice strain reduces as an anti-sigminoidal behaviour while the average size of the crystallite grows as a sigminoidal behaviour as the annealing temperature is raised.
The optical energy gap in the high area of the absorption was computed using the T and R spectra. With an increase in the various annealing temperature, the energy gap falls from 1.50 to 1.37 eV. The addition of Cu ions in the lattice, which causes the rise in the bandgap acceptor levels, may be the cause of the reduction in the energy gap. The bandgap is reduced as a result of the valence band expanding into the forbidden region as a result of the acceptor rates descending and joining together.