  We report the results of an analysis, based on a straightforward
quantum-mechanical model, of shot noise suppression in a structure containing
cascaded tunneling barriers. Our results exhibit a behavior that is in sharp
contrast with existing semiclassical models for this particular type of
structure, which predict a limit of 1/3 for the Fano factor as the number of
barriers is increased. The origin of this discrepancy is investigated and
attributed to the presence of localization on the length scale of the mean free
path, as a consequence of the strictly 1-dimensional nature of disorder, which
does not create mode mixing, while no localization appears in common
semiclassical models. We expect localization to be indeed present in practical
situations with prevalent 1-D disorder, and the existing experimental evidence
appears to be consistent with such a prediction.
