Scattering of a two-dimensional electron gas by a correlated system of ionized donors

Using selectivity doped GaAs-AlGaAs heterostructures we provide conclusive evidence that correlation among the DX - -d + charged donors strongly enhances the mobility of a two-dimensional electron gas (2DEG) residing 10 nm away from the charged donors. This is accomplished by changing the extent of correlation without affecting the total number of charged donors and density of electrons in the 2DEG. The experiments are used to prove that the DX donors are negatively charged in their ground state. A theory treating correlated DX - -d + charges can approximately account for these results.