Unified approach to electron transport in double-barrier structures

In this paper we show an approach to electron transport in double-barrier structures that unifies the well-known sequential and resonant tunneling models in the widest range of transport regimes, from completely coherent to completely incoherent. In doing so, we make a clear distinction between ''approaches'' and ''transport regimes,'' in order to clarify some ambiguities in the concept of sequential tunneling. Scattering processes in the well are accounted for by means of an effective mean free path, which plays the role of a relaxation length. Our approach is based on a recently derived formula for the density of states in a quantum well, as a function of the round-trip time in the well and of transmission and reflection probabilities for the whole structure and for each barrier.