  A technique is developed which allows for the detailed mapping of the
electronic wave function in two-dimensional electron gases with low-temperature
mobilities up to 15E6 cm^2/Vs. Thin ("delta") layers of aluminium are placed
into the regions where the electrons reside. This causes electron scattering
which depends very locally on the amplitude of the electron wave function at
the position of the Al "delta"-layer. By changing the distance of this layer
from the interface we map the shape of the wave function perpendicular to the
interface. Despite having a profound effect on the electron mobiliy, the
"delta"-layers do not cause a widening of the quantum Hall plateaus.
