Transport Properties Of A Quantum Dot With Electron-Phonon Interaction

The electronic transport properties of mesoscopic systems (such as quantum dot, quantum wire or nanowire) have been paid much attention. These properties are not only important basic problems of physics but also have potential applications in the future. The quantum dot and quantum wire etc., will be very important parts of the nanocircuit. Recently, the structure of the quantum dot has been studied intensively by many authors because of its typical quantum effect in all the low-dimensional mesoscopic systems. In this thesis, within the framework of effective-mass free electron approximation and using the Keldysh nonequilibrium Green function approach, we investigate theoretically the electron transport properties of a semiconductor heterojunction quantum dot with electron-phonon interaction. And some interesting new results have been predicated for the system.The thesis consists of five chapters. In chapter one we briefly introduce the both history and present of studies about the quantum dot. The particular electron transport properties of the quantum dot (such as Coulomb blockade, single charge tunneling) have developed the area of the design and manufacture of nanostructures. Many works about the quantum dot in the presence of electron-phonon interaction are mainly focused on theory study rather than experiment. Chapter two describes the formation of semiconductor heterojunctions from the theory of energy bands, and the fabrication as well as the usage of quantum well, quantum wire and quantum dot based on these heterojunctions. Meanwhile, several mesoscopic phenomenon of the low-dimensional systems have been discussed. Chapter three introduces the nonequilibrium Green function method and its applications in mesoscopic transport, and the widely-employed Keldysh equation of motion with a current formula are induced.The content of chapter four is mainly our work. The knowledge about phonon and electron-phonon interaction is presented. Using the method of Keldysh nonequilibrium Green function, we have studied the electronic transport properties of a quantum dot with the electron-phonon interaction. The conductance of the system appears many interesting sideband peaks (satellite peaks) with electron-phonon interaction while only a single resonant peak turns up without the electron-phonon interaction. This is the phonon-assisted tunneling. As the strength of electron-phonon interaction increases, more sideband peaks appear and the height of the main peak decreases; As the temperature increases, the sideband peak becomes sharper and the height of the main peak also decreases. These phenomena are qualitatively discussed in detail.In chapter five, a summary of the work and a outlook of this topic are given.