Quantum Hall Samples: Role of Contacts


Top-view scanning electron microscope image of alloyed Au/Ge/Ni metal contact to two-dimensional electron system in an (Al,Ga)As heterostructure. © MPI-FKF / O. Göktas

The quantum Hall effect is measured by probing voltage drops between metal contacts attached to the two-dimensional charge carrier system. Indeed, the properties of these ohmic contacts play a significant role what Hall resistance value is measured.

We have developed a recipe which allows to contact two-dimensional electron systems in (Al,Ga)As heterostructures reliable by alloying Au, Ge and Ni. Striking is the dependence of the contact resistance on the orientation of the borderline between 2DES and alloyed metal relatively to the underlying crystal directions. Detailed scanning force microscope investigations on various Hall bar configurations showed that different partial electrostatic depletion of the 2DES in front of metal contacts affects the possible Hall potential and therefore current distribution inside the 2DES.


Adiabatic transport and Hall potential measurements in the integer quantum Hall effect
F. Dahlem, E. Ahlswede,  J. Weis, K. v. Klitzing
AIP Conference Proceedings 893, 675 (2007)

Cryogenic scanning force microscopy of quantum Hall samples: Adiabatic transport originating in anisotropic depletion at contact interfaces
F. Dahlem, E. Ahlswede, J. Weis, K. v. Klitzing
Physical Review B 82, 12 (2010)

Alloyed ohmic contacts to two-dimensional electron system in AlGaAs/GaAs heterostructures down to submicron length scale
O. Goektas, J. Weber, J. Weis, K. von Klitzing
Physica E 40, 1579 (2008)


Adiabatic transport in the quantum Hall regime: Comparison between transport and scanning force microscopy investigations
Franck Dahlem, Dissertation, Universität Stuttgart (2008)

Small alloyed ohmic contacts to 2DES and submicron scale Corbino devices in strong magnetic fields: observation of a zero bias anomaly and single-electron charging
Oktay Göktas, PhD Thesis, Universität Stuttgart (2009)

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