Although Pd/Ti/Pd/Au contacts are similar to their Pt/Ti/Pt/Au counterparts
in providing low specific contact resistance, rho(c), the former exhibits
long-term thermal stability. Their projected mean times to 50% increase in
rho(c)(mu(50)) at 150 degrees C to p(+)-GaAs (greater than or equal to 3.43
x 10(15) h) are higher than those of the latter by over five orders of mag
nitude. Contacts to p(+)-In0.53Ga0.47As are not as thermally stable, with a
much lower albeit respectable mu(50) at 150 degrees C of greater than or e
qual to 2.25 x 10(5) h. Contacts with an interfacial Pd layer provide rho(c
)'s that are at least two times lower than those without, and the presence
of an oxide layer (GaxTiyOz) at the Ti/GaAs interface is identified as a po
ssible cause. Pd-Ga-As phases are formed at the Pd/GaAs interface, being As
-rich (PdxGayAs) initially and convert to Ga-rich phases (PduGavAs) upon a
high temperature anneal and the eventual composition depends on the evapora
ted interfacial Pd thickness and annealing conditions. This could probably
explain the existence of an optimum interfacial Pd layer thickness of 100 A
ngstrom for achieving the lowest rho(c). The Ga-rich PduGavAs phases formed
are inferred to cause the liberation of As atoms from the GaAs lattice, th
us enabling them to diffuse out to the Ti and react to form TixAsy phases t
hat bind the As from further out-diffusion. This has in turn led to the acc
umulation of As at the Pd/Ti interface. (C) 2000 American Institute of Phys
ics. [S0021-8979(00)02705-5].