LOW-TEMPERATURE OPERATION OF GE-AG OHMIC CONTACTS TO A HIGH-MOBILITY 2-DIMENSIONAL ELECTRON-GAS

Ge-Ag ohmic contacts with good dimensional control to a two dimensiona l electron gas operating at low temperatures are demonstrated. At 4.2 K, the specific contact resistance lies in the range 2-5 OMEGA mm for anneals between 520 and 560-degrees-C. The surface morphology is smoot h, and the edge definition is of the order of 100 nm. Secondary ion ma ss spectroscopy analysis indicates that Ge diffusion is limited to wit hin 2000 angstrom of the surface for a concentration of 10(17) cm-3 in samples annealed at 540-degrees-C and below.