transport properties (or low-temperature transport properties) with the temperature being much smaller than both the Fermi temperature and the Bloch-Grüneisen (BG) temperature of the 2D system so that all thermal effects have saturated, and we do not need to account for either phonon scattering or finite temperature effects in the Fermi distribution function. The high mobility of 2D semiconductor structures applies only to this low-temperature situation, and at higher temperatures ($>10$K), the mobility is dominated by phonon scattering, a situation already well-studied in the literature[@stormerbg]. Our theory is just restricted only to $T=0$ impurity-scattering-limited 2D transport properties, which limit the ultimate achievable mobility in these systems. It is also important to emphasize that we ignore all weak localization aspects of 2D transport properties, restricting entirely to the semiclassical transport behavior where the concept of a mobility is valid. Thus, the theory applies only at densities where weak-localization behavior does not manifest itself at the experimental temperatures ($\sim 25$ mK $- 2$ K). At a fixed density, this limits our theory to a temperature high enough ($>1$ mK) so that the phase breaking length is shorter than the semiclassical mean free path. The physics of mobility/quality dichotomy discussed in this paper 