Fabrication of quantum Hall devices for low magnetic fields

The quantized Hall resistance of a two-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures is used for the realization of the unit of resistance. This effect is more and more widely used. For possible application even in magnets with magnetic flux densities as low as 6 T, such devices have been produced with carrier concentrations in a range from 2.7/spl times/10/sup 15/ m/sup -2/ to 5.4/spl times/10/sup 15/ m/sup -2/ and their metrological quality has been checked. We find that even in low magnetic fields the quantized Hall resistance can be reproduced with highest accuracy.