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An analytic approach to the real-space transfer in semiconductor superlattices with highly doped barriers

The parallel transport in semiconductor superlattices and the associated transfer of electrons from high- to low-mobility layers are treated on the basis of quantum kinetic equations. Due to the assumed dominant role of impurity scattering in the barriers, the description of transport properties simplifies considerably. The superlattice band structure is replaced by a two-band model that simulates electronic states in the narrow quantum wells and in the adjacent broad barriers. Using the quasi-elastic approximation for the electron - phonon scattering in the narrow miniband, analytical results are derived for the current density that provide a qualitative understanding of the main physics taking place in the device. The approximate description of the real-space transfer encompasses scattering on acoustic and optical phonons as well as on impurities. Particular emphasis is put on the negative differential resistance and its dependence on the well width.