Theoretical Study Of The Superlattices, Transport And Kinetic Issues

In this thesis, we have some theoretical studies of transport and dynamics in superlattices. We focus on some phenomena: response current, dynamic localization, Rabi oscilliations, the formation of electic field domains, and effect of external noise.In chapter.2, within a single-band tight-binding model , we investigate the effect of external noise on the current response driven by dc-ac field which has a fluctuating component. We find the external noise can destroy the current resonant peaks. When rhe strength of the external noise becomes enough large, all the current resonant peaks will completely disappear.In chapter.3. within a single-band tight-binding model, we investigate the property of dynamical localization of a one-dimensional semiconductor superlattices under a dc-bichromatic electric field. We obtain analytically the quasi-energy spectrum of the system and the conditions of dynamical localization. The results show that they depend sensitively on the frequency ratios, wB/w1 and w2/w1 where wb is the Bloch frequency, w1 and w2 are the external electric field frequencies. For the case in a bichromatic ac field (wb = 0). the dynamical localization happens at the quasi-energy band collapse points. For the case in a dc-bichromatic electric field (wB= 0), when one of the ratios is an irrational number, the other is a rational number, the dynamicallocalization always remains. When both the ratios are rational or irrational numbers, the dynamical localization happens at the quasi-energy band collapse points.In the chapter.4, With a two-band tight-binding model drivened by dc-ac electric fields, we investigate the transport characteristics of Rabi oscillations between Bloch bands. Firstly, we foucus on the relation of Rabi oscillation mechanism and current response, and find Rabi oscillation can make current have a sharp change. Secondly, inthe case of the weak interband coupling, Rabi oscillation and current peaks appear at = mw or = mwB (m, n is integer): in the case of the strong interband coupling, Rabi oscillation and current peaks appear at the places which have a deviation from = mw or = mwB.In the chapter.5, within the framework of sequetial tunneling, by a phenomenological model of strong field and weakly coupled superlattices, we draw some phase diagrams which show a transition process from static to dynamic electric-field domain formation. During this transition, it can be noticed that a sawtooth-like zone in which static and dynamic electric-field domain zone appear alternatively with increasing voltage. Therefore, a dynamic dc voltage band emerges from each sawtooth-like branch of the current-voltage characteristic. These results are qualitatively in agreement with experiment.