Abstract
A single impurity is used to probe the local density of states of a two-dimensional electron gas (2DEG) in a resonant tunneling experiment. The studies have been performed in the GaAs/AlAs/GaAs system, with Si donors incorporated into the AlAs layer, on submicrometer junctions. The current-voltage characteristics clearly show peaks corresponding to the formation of Landau levels. Moreover, additional fine-structure superimposed on the Landau levels are resolved. Detailed magnetic field studies suggest that those peaks reflect the single particle states of the Landau levels. The surprisingly rapid shift of these additional features in a magnetic field is reproduced in a model, which takes into account disorder in the plane of the 2DEG.