Vertical transport and domain formation in multiple quantum wells

Abstract

In this book article effects related to the vertical transport in weakly coupled multiple quantum wells are reviewed. A self-contained microscopical model for the calculation of the well-to-well currents without any fittings parameters is presented. The model exhibits the well-known peaks in the current-field relation in quantitative agreement with experiments. This local current-field relation is used as an input for the calculation of the transport in the extended structure consisting of many periods. Here both the formation of stationary field domains as well as self-sustained current oscillations are found in good agreement with experimental data. The underlying physics of these nonlinear phenomena is discussed in detail.

Intersubband gain in a Bloch oscillator and quantum cascade laser

“…The populations may be described by thermal distributions, either by Fermi-Dirac or Boltzmann statistics. The current-voltage characteristic resembles the Esaki-Tsu characteristic and agrees quantitatively with the result by Wacker et al 16 within the sequential tunneling picture 17 valid for weakly coupled superlattices. This assumption is implicit in the present approach, as we allow only for next-neighbor interaction and multiple tunneling is excluded, corresponding to a limited coherence of spatially extended states.…”

Semiconductor superlattices: a model system for nonlinear transport

“…Nevertheless different current signals have been observed as well, both experimentally and in numerical simulations (see, e.g., Fig. 10.12 in [35] for results obtained from the same model with different boundary conditions). The oscillations reported here are due to traveling high-field domains which is different from the calculations presented in [181,186,187] where traveling monopoles have been reported.…”

“…For doped superlattices ionized impurity scattering dominates and the respective calculations including screening are presented in [120,35]. Scattering processes at interface roughness [35] and phonons have been considered as well.…”

“…As explained in [35,184,196] this leads to stationary domain states, provided the transition region between the two domains becomes of the order of the superlattice period. In this case the accumulation or depletion front gets trapped within one well.…”

Electric field domains in p-Si/SiGe quantum cascade structures

“…The effect is related to the existence of negative differential resistivity (NDR) of the heterostructure, and is detrimental for the normal operation of devices. The problem of domain formation has been addressed in a number of papers [2], [6]- [17], and methods of avoiding it have also been considered recently [18]. The NDR is usually ascribed to resonant tunneling between quantized states in neighboring wells.…”