Independent contacting to electron layers in a double quantum well system using Pd-Ge shallow ohmic contacts

Abstract

A novel recess technique is used to produce reliable Pd-Ge ohmic contacts to GaAs/AlGaAs high mobility two-dimensional electron gas (2DEG) systems, operating down to cryogenic temperatures. By altering the depth of the recess the diffusion length of the contacts is found to be less than 20 nm. Pd-Ge shallow ohmic contacts were also used for forming independent contacts to two 2DEGs in a double quantum well structure where the 2DEGs are separated by only a 20 nm AlxGa1−xAs(x=0.3) barrier. Tunnel current measurements and magnetoresistance analysis confirmed that the layers could be probed individually and that the carrier densities and mobilities of the separate layers could be accurately determined.