  We discuss the possibility of diffusive conduction and thus of suppression of
shot noise by a factor 1/3 in mesoscopic semiconductor devices with
two-dimensional and one-dimensional potential disorder, for which existing
experimental results do not provide a conclusive result. On the basis of our
numerical analysis, we conclude that it is quite difficult to achieve diffusive
transport over a reasonably wide parameter range, unless the device dimensions
are increased up to the macroscopic scale. In addition, in the case of
one-dimensional disorder, some mechanism capable of mode-mixing has to be
present in order to reach or even approach the diffusive regime.
