Highly precise quantized resistance values are nowadays reproduced by means of the Quantum-Hall Effect (QHE) in two-dimensional conducting layers (2DEG) made from semiconductor heterostructures. The new kind of semiconductor structures fabricated at PTB consist of even two conducting layers stacked on top of each other, both having equal electrical properties. Such optimized double-2DEG structures form the building blocks for integrated circuits of QHE elements connected in parallel on one chip in order to realize decade resistance values and to establish a quantum OHM-scale. The vertical integration simplifies the lateral circuit and an improved fabrication yield is expected. High precision QHE measurements have shown that the new semiconductor structure with two identical 2DEG layers connected in parallel provides a resistance value which agrees with the theoretically expected value of the von-Klitzing-constant RK/4 ~ 6453 Ω to within an accuracy of 10-9. This accuracy is similar to the one which is usually obtained from single Hall devices. The results are presented at the International Conference on Precision Electromagnetic Measurements (CPEM) in June 2008 in Broomfield/USA. More details can be found in a recently published article in Applied Physics Letters 92 133509 (2008).

Fig.1 Newl asymmetric double 2DEG-Structure. Top: schematic valence band profile Ec indicatin the two conducting sheets HJ- und QW-2DEG. Bottom: Carrier density profile.

Fig.2 The Hall resistance RH in dependence on magnetic field B of a double 2DEG device equals in ist working point (plateau i = 2) exactly RK/4 ~ 6453 Ω . The longitudinal conductivity Ρxx is zero.