Ionized donor reordering in typical heterostructures

The mobility of the 2-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures is limited by the presence of ionized donors in the doped region, which determines random potential fluctuations in the 2DEG. However, especially at very low temperatures, only a fraction F of all dopants is ionized. When this fraction is significantly less than unity, redistribution of the ionized sites through hopping can lead to reordering of the donor layer charge and thus to larger than otherwise expected 2DEG mobility. Here we evaluate the relevance of this effect in some typical heterostructures, and look for criteria for the achievement of the largest possible mobility.