CORRELATED CHARGED DONORS AND STRONG MOBILITY ENHANCEMENT IN A 2-DIMENSIONAL ELECTRON-GAS

Using selectively doped GaAs-Al0.37Ga0.63As and GaAs-AlAs heterostructures, we provide conclusive evidence for correlations among charged donors, DX--d+ in Al0.37Ga0.6,As and d+-d0 in AlAs, which strongly enhance the mobility of a two-dimensional electron gas (2DEG), residing 10 nm away from the charged donors. The determination was accomplished by changing, in the same structure, the extent of correlations without affecting the total number of charged donors and density of the 2DEG. An approximate theory accounts for the measured mobilities.