الفهرس 
Chapter I: IntroductionOnly 14 pages are availabe for public view
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Abstract
In this work we study the quantum effects in mesoscopic system. Transport characteristics for such mesoscopic systems are investigated theoretically by considering two different models of the Superconductor-Semiconductor-Superconductor junction. The first model for the junction is in the form of sandwich type and the second model is superconducting quantum point contact (SQPC).
For the first model, the transport characteristics through Superconductor-Semiconductor-Superconductor (S-Sm-S) junction is investigated on the basis of the WKB approximation. The Schottky barrier effect at the Superconductor-Semiconductor interface is taken into account. Expression for lie current density is obtained, taking into consideration the Andreev reflection.
It is found that the electrical junction characteristics are strongly influenced by the microstructure of the barrier itself. Our expression shows the temperature dependence of the current density. The results of our theory fit nicely the available experimental data.
For the second model, superconducting quantum point contact with a mesoscopic constriction made of semiconductor is investigated. The effect of both multiple Andreev and normal reflections at the superconductor -semiconductor interface is taken into consideration. The junction is studied in the clean limit and high mobility of the electron carrier . These considerations show that the electrons can travel ballistically .The current has been derived by solving the Bogoliubov-de-Gennes (BdG) equation and finding the scattering amplitudes due to both Andreev and normal reflection.
It is shown that the critical current is quantized and increases stepwise as a function of the width of the semiconductor layer and the doping concentration up to certain values of both . After the limit of quantization of the current, the behavior of its variation seems to be a δ- function behavior. These results found a good concordant with results obtained by other authors.
In general, the electrical properties of such mesoscopic system depend both on the nature of the S-Sm interface and on the coherence length in the semiconductor channel. The coherence length could be controlled by varying the doping concentration in the semiconductor. Such investigations on mesoscopic systems might be valuable for nanotechnology of nanoelectronic devices.
The thesis contains four chapters. The first one reviewed the historical works on sandwich and quantum point contact junctions both experimentally and theoretically. The second chapter treats the theory of the sandwich and SQPC junctions in mesoscopic systems. The numerical calculations and results is given in chapter three and chapter four summarizes the main conclusions.