Hot-electron transport in a GaAs-AlGaAs heterojunchon is studied by the use of a non-Boltzmann balace-equation approach recently developed. The occupation of the lowest and next lowes subbands and coulomb interactions between inrasubband and intersubband elelctrons are taken into account. We include the scattering by remote charge impurities, acoustic phonos (via deformation potential and piezoeletric coupling), and polar opteical phonons in the force and energy balance equations to give the carrier mobility as a function of dirft velocity and/or eletric field. Theoretical results are in reasonably good agreement with experiments.

A non-Boltzmznn theory of steady-state transport for two-dimensional systems in a strong electric field is developed, which includes a force-and an energy balance equation. The electron termperature, impurity-, and phonon-limited mobilities are determined solely from these balance equations. The theory is applied to the calculation of ohmic and nonlinear transport in GaAsGaAlAs heterojunctions at low temperatures. Temperature-dependent ohmic mobilities are calculated and compared with experiments. Nonlinear effects in electronic transport at low temperatures are discussed and some numerical results are presented. We also compare the present balance equations with those in the carrier temperature mode).

A Green's function approach to nonlinear electronic transport in a static electric field is developed microscopically for the system composed of interacting electrons with impurities and phonons. The essemtoal idea is to separate the center-of-mass motion of electrons. An electron temperature is introduced as a measurement of the internal energy of the relative electrons electrons and phonons in the initial state, we obtain the density matrix for the electron-lattice sysytem to the first order of mass of interaction but nuder arbitrarily strong electric field. The frictional force experienced by the center of mass of the Green's-function technique, and the force-and energy-balance equations for steady state are obtained. These equations are qpplied to the calculations of the ratio of electron temperature to the lattice temperature and the electron redsistivity as functions of drift velocity imputity, acoustic-phonon, and optcal-phonon scatterings. The dynamic nature of Coulomb screening by charge carriers is studied numerically. One of the interesting predictions is the possible cooling of electtons at low temperatures in samples with low impurity comcentration.

The nonlinear transport for interacting electrons with phonons and impurities is studied in the presence of a strong electric field E. By separating the center-of-mass motion from the relative motion of electrons we are able to obtain force-and energy-balance equations in steady states, form which the electron temperature and current density can be determined self-consistently as a function of E.

Microwave-radiation induced giant magnetoresistance oscillations recently discovered in highmobility two-dimensional electron systems are analyzed theoretically. Multiphoton-assisted impurity scatterings are shown to be the primary origin of the oscillation. Based on a theory which considers the interaction of electrons with electromagnetic fields and the effect of the cyclotron resonance in Faraday geometry, we are able not only to reproduce the correct period, phase, and the negative resistivity of the main oscillation, but also to predict the secondary peaks and additional maxima and minima observed in the experiments. These peak-valley structures are identified to relate, respectively, to single-, double-, and triple-photon processes.