We investigate the effect of a uniform intense terahertz radiation on hot-electron transport in semiconductors driven by a dc or slowly varying electric field of arbitrary strength. Using a vector potential for the high-frequency field and a scalar potential for the dc or slowly varying field, we are able to separate the center-of-mass motion from relative motion of electrons and to distinguish the slowly varying part from the rapidly oscillating part of the center-of-mass velocity. Considering the fact that relevant transport quantities are measured over a time interval much longer than the period of the terahertz radiation field, we obtain a set of momentum and energy balance equations, without invoking a perturbational treatment of the electron-photon interaction. These equations, which include all the multiphoton processes, are applied to the examination of hot-carrier transport in a GaAs-based quantum well subjected to a weak or a strong dc bias and irradiated by a terahertz radiation of various frequency and strength in both the parallel and vertical configurations. Up to as many as unu 550 absorption and emission multiphoton channels are included in the numerical calculation. The present approach turns out to be a very convenient and efficient tool to study the effect of an intense high-frequency radiation on dc or slowly varying carrier transport in semiconductors. Its applicable frequency range and its connection with previously developed balance-equation treatment are discussed.

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).

Bloch electron conductivity perpendicular to the layers of a superlattice (period d) is evaluated using an extension of the balance-equation qpproach [X.L. Lei and C.S. Ting. Phys. Rev. B 32, 1112(1985)] to narrow-band transport. The perpendicular park drift velocity Tp and The critical field Ec, at which the drift velocity peaks, are analyzed as functions of miniband width. Our theoretical predication that Ecd increases with decreasing miniband width agrees well with the data of Sibille et al. [Phys. Rev. Lett. 64, 52(1990)], even for the samples of narrowest miniband width in their expriment.

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.

The balance-equation approach developed by Lei and Ting for steady-state hot-electron transport is extended here to include nonequilibrium phonon occupation under the assumption that the effect of phonon-phonon interaction can be represented by an effective phonon relaxation time Tp, which may be mode dependent. Both single heterojunctions and multiplayer quantum-well superlattices, as well as three-dimensional (3D) bulk systems, are discussed. A 3D phonon model and a quasi-2D phonon model are employed in describing the various interaction electron-phonon systems. The expressions for the frictional forces and energy transfer rates obtained in steady state are structurally similar to those without hot-phonon effects and the balance equations with finite phonon relaxation can be solved with the same computational effort as in the case of Tp=0. We have examined hot phonon effects on the energy-transfer rate, the electron temperature, and the linear and nonlinear mobilities. It is given lattice temperature. However, It significantly increases the velocities. For an n-type GaAs heterosystem the normalized electron-energy-loss rate at Tp=3.5ps is seen to be a factor of 5-10 smaller than that at Tp=0. The functional dependence of the energy-loss rate on carrier temperature shows considerable difference form the prediction of a carrier temperature-type theory, and is in reasonably good agreement with experiments.