Too La Hezi Field And Strong Magnetic Field Under The Action Of The Transport Properties Of Semiconductor Super-lattice System

Transport in semiconductors in the presence of a strong magnetic field has been an inter- esting problem for a long time. Up to now, high magnetic fields have continued to be a valuable tool in semiconductor research. The electron energy spectrum in a uniform magnetic field becomes partially discrete, the circular electron motion is quantized in a plane perpendicular to the field. This Landau quantization causes many effects to transport properties of semi- conductor systems. The main approaches of studying the magnetic transport properties, the Boltzmann equation theory and the Kubo formula, are limited in linear regime and very hard to extend beyond linear conduction. The balance equations theory, developed by Lei and Ting a decade ago, based on the separation of the center-of-mass motion from the relative motion of electrons in Hamiltonian and in density matrix, has the advantage of describing nonlinear transport. Because of its simplicity of mathematical structure, its generality of description of nonlinear transport and its ease of treating dynamic, nonlocal intercarrier coupling, it becomes very effective and useful method of transport study. In this thesis, the balance equations theory in strong magnetic field was introduced. Electron transport of semiconductor systems under intense radiation fields of terahertz (THz) frequency have been the subject of many theoretical and experimental studies in the literature for the past several years. To deal with the transport properties of the intense THz- driven semiconductor systems the perturbative treatment of electron-photon interaeton will be no longer valid. Recently, several nonperturbative approaches have been developed. The balance-equation approach as one of them provides convenient tools to investigate the nonlinear transport of semiconductor systems. We will concisely introduce the balance equations under the influence of high frequency radiation field. It has been predicted recently that multiphoton-magnetophonon resonant peaks may show up in the magneto-resistance of a two-dimensional polar semiconductor subject to a dc mag- netic field and a crossed THz radiation field. For miniband transport of electrons in a polar- semiconductor-based superlattice with narrow bandwidth, Shu and Lei pointed out a few years ago that quantized magnetic fields parallel to its growth axis may induce strong oscillation of linear mobility and drastically change of the velocity-field behavior when polar-optic-phonon scatterings are resonantly enhanced or forbidden due to Landau quantization of energy levels. In particular, when the gap between neighboring Landau levels is large enough that the polar- optic phonon scattering is forbidden, the peak drift velocity of miniband conduction may become quite small due to strongly enhanced electron temperature. Such a magnetic-field quenching of miniband conduction has recently been observed experimentally in quasi-one-dimensional superlattices. In this thesis, linear and nonlinear transport properties of electrons in GaAs-based su- perlattices under an intense terahertz radiation field and a parallel magnetic field are studied. Based on the recently developed balance equations for terahertz (THz)-driven transport in a quantized magnetic field, we calculated the linear mobility driven by a small dc electric field and the drift velocity and electron temperature in high electric fields, as function of the magnetic field. Impurity, acoustic, and polar-optic-phonon scatterings are taken into account. As many as 31 Landau levels are included in the calculation.