Theoretical Study On Electronic Transport Properties Of Coupled-Quantum-Dot System

Quantum dot is a new kind of low-dimensional quantum structure, which, together with quantum wire, is developed after superlattices and quantum well in the late 80's of last the century. Several quantum dots form a coupled-quantum-dot system when they close up and couple to each other by tunnel coupling. For coupled-quantum-dot systems, no matter the spatial symmetry, size and tunnel coupling strength between quantum dots are all controllable. In this way, the dream of controlling solids is realized. For this reason, the transport properties of systems consisting mutiple quantum dots have attracted the interest of physicists. In this thesis, by making use of the nonequilibrium Green's function technique, we investigated the transport properties of several new kinds of coupled-quantum-dot systems theoretically and obtained several significant results.First, we report a theoretical study of an ideal ring-shaped array of quantum dots (quantum-dot ring for short) in a two-terminal configuration. For a quantum-dot-ring, the dots connected to the leads are special than the others. So we discuss three different configurations with the two leads being connected to the same dot, to two adjcent dots, and to two unadjcent dots. By making use of the equation of motion and Dyson equation of Green's functions, we have developed a theoretical method for a quantum-dot ring with arbitary number of dots. As an example, we numerically investigated the transport properties of a four-quantum-dot ring. We found that the resonant tunneling spectrum depends on the arrangement of the single-dot energy level, the interdot tunnel coupling amplitude between neighbouring dots, and the tunnel coupling between dots and leads. The study shows that all these parameters have strong influence to the transport properties of the system.With the increasing of the number of dots, the resonant tunneling spectrum becomes more complex. When we disscuss the n-dot system, for simplicity, we assume all quantum dots are all equivalent, i.e. all the single-dot energy levels are...