With the advances of fabrication techniques, the crossover region between these two fundamental regimes has been the subjects of intense experimental and theoretical investigation. The system that falls into this crossover region is called mesoscopic region and this system is small enough in physical size that its behavior reveals quantum-mechanical effects, although it contains a macroscopic number of particles. In other words, whenever the size of a physical system becomes comparable to the wavelength of the particles that interact with such a system, the behavior of the particles is best described by the rules of quantum mechanics. All the information we need about the particle is obtained by solving its Schrodinger equation. The solutions of this equation represent the possible physical states in which the system can be found.