Study of the Quantized Hall Effect as a Resistance Standard at ETL

Study of the quantized Hall effect as a resistance standard at ETL is in progress. The quantized Hall resistances (QHR´s) have been measured using AlGaAs/GaAs modulation doped (MD) structures, that have been made at ETL, and Si-MOSFET´s. The measurements were carried out at magnetic fields of 7 T for a GaAs sample (i = 2) and 15 T for a Si sample (i = 4) at a temperature of 1.3 K. The QHR value was 25 812.8025 ??ETL (?? 0.13 ppm), determined using a Si-MOSFET. The QHR value of an AlGaAs/GaAs MD device was 0.06 ppm smaller than that of the Si-MOSFET. The difference in QHR values between Si and GaAs samples was within the total uncertainty of our measurements. An apparent difference in QHR values cannot be found between materials or between Landau numbers within our measurement uncertainty. A new AlGaAs/GaAs SIS structure, in which the density of the two-dimensional electron gas can be changed by variation of gate voltage as in a Si-MOSFET, is introduced as an excellent candidate for a future device that can realize the QHR at much lower magnetic fields.