For the contact resistance evaluation, Ge/Pd (150 nm/15 nm)
layers were deposited on the n-type GaAs substrate and Pt/Ti/Pt
(60 nm/50 nm/5 nm) layers were deposited on the p-type Ge substrate
by E-gun evaporation. Cu (150 nm) was then sputtered on
the samples afterward and the contacts were formed by lift-off
method as showed in Fig. 1. Then, the samples were annealed by
RTA method from 100 C to 390 C for 30 s in an N2 atmosphere
to obtain the optimum annealing temperature. The diffusion profiles
of the layers were examined using Auger depth analysis. The
specific contact resistances were determined by transmission line
model measurement.
The thermal stress tests were performed for a duration from 3
to 9 h. The electrical stress test was performed with a continuous
biased DC current with density of 6.5 104 mA/lm2 for a duration
from 3 to 9 h. Finally, the contact resistances were measured
after the thermal and electrical treatments to evaluate the stability
of the contacts.