CONTACT RESISTANCES OF NIGEAU, PDGETIPT, AND TIPD OHMIC CONTACTS TO GAAS AND THEIR TEMPERATURE-DEPENDENCE FROM 4.2 TO 350 K

The specific contact resistance (r(c)) of NiGeAu and PdGeTiPt ohmic co ntacts to n-GaAs and TiPd and PdGeTiPt ohmic contacts to p(+)-GaAs wer e determined as a function of temperature between 4.2 and 350 K. The l ow r(c) obtained for some of the contacts at 4.2 K implies that much o f the total contact resistance measured at 4.2 K in two-dimensional el ectron gas structures lies across the n-n heterojunction(s) in series with the metal semiconductor junction. Although NiGeAu contacts have a lower contact resistance to n-GaAs, PdGeTiPt contacts, which have muc h better edge definition, can be substituted for the NiGeAu when they are properly annealed. Also, contacts with low r, values at 4.2 K can be made to p(+)-GaAs using either TiPd or properly annealed PdGeTiPt c ontacts. The r(c) versus temperature curves for the TiPd and alloyed N iGeAu contacts fit the field emission model. The other contacts have a larger temperature dependence suggesting that tunneling occurs via th ermionic held emission directly through the barrier or via defect stat es. (C) 1996 American Institute of Physics.