The Electronic Transport Properties Of Y-type Quantum Switch

Only in 20 years since the late 1980s? mesoscopic physics, one burgeoning subject of Condensed States Physics, quickly comes into being and becomes a new hotspot of the studies in Condensed States Physics. Because of the widespread applications of mesoscopic devices in micro-electronics technology and integrate circuits and so on, more and more attention has been paid to the research of those in many countries. In this paper detailed investigations have been extended to the electron transport properties of the Y-shaped quantum switches formed on the heterostructure of GaAs and A1GaAs and the quantum bound states in the structures by the transfer-matrix method and the scattering- matrix method. Some typical effects including weak localization effect, universal conductance fluctuations, coulomb blockade effect, Ahoronov-Bolm effect, and integer and fractional quantum Hall effect have been introduced briefly in Chapter 1. In Chapter 2, the of two dimensional electron gas in heterostructures and the state density of the low dimensional electron gas are presented. we introduce some important characteristic lengths such as Fermi length, mean free path, phase-relaxation length and so forth. We also give the conditions in which electrons transport ballistically and derive the basic Landauer ?Btiker conductance formula in mesocopic physics. At last the quantum bound states in bent-structure are presented. The theoretical methods used in this paper, namely, the mode-matching method, the transfer-matrix method and the scattering-matrix method. are presented in Chapter 3. Chapter 4 is contributed to the numerical analysis on Y-shaped structures. The contents of this chapter include the transport properties of the Y-shaped quantum switches and the forming conditions for switching. We demonstrate that one of the two channels of the Y-shaped quantum switch is open, and the other is closed when electric field is strong enough. If the electric field is reversed, the opposite case will happen. Quantum bound states in Y-shaped quantum structures are investigated in Chapter 5. In our studies, the Y-shaped quantum structures are classified into three types: T-S shaped structure, symmetric Y-shaped structure and asymmetric Y-shaped structure. The following three results can be achieved: 1) In T-S shaped structures, there exist two coupling quantum bound states and the conductance peaks are related to the resonant tunneling through them. The energy of bound states can be obtained by the perturbation theory. 2) In symmetric Y-shaped structures, there are only two conductance resonant peaks under the first mode. The bound state which corresponds to the first peak mainly locates on the middle bend area, while the other bound state mainly locates on the two up-and-down bend areas. The probability distribution is symmetric about x axis and the second energy level is 2-fold degeneracy. 3) In asymmetric Y-shaped structures, three conductance resonant peaks can be found under the first mode, that's to say, there are three bound states. In this case the degenerate energy level is splitted.