Microscopic balance equations for the real-space transfer in multiple quantum wells

Abstract

The parallel electronic transport in semiconductor multiple quantum wells and the associated real-space transfer of electrons from high-mobility quantum wells into low-mobility barriers is treated on the basis of the microscopic Lei-Ting balance-equation theory. Our model system consists of a quasi-two-dimensional subband that is bound to the wells and a quasi-three-dimensional band for the extended states above the barriers. The real-space transfer between the two subbands is microscopically described as intersubband scattering by phonons. In order to capture the appropriate selection rules for these transitions, it is necessary to choose a set of orthogonal subband wavefunctions. A solution of the balance equations is presented for a system in which the real-space transfer causes negative differential resistance. Our approach shows how the transport properties of the system are interrelated with the different transfer scattering processes, and how system parameters influence the real-space transfer. Furthermore, it is shown that the incorporation of screening requires a careful selection of the screening model, as both intersubband contributions and dynamical effects are found to modify the results in the random-phase approximation.