Results and discussion
The specific contact resistance was derived from the current–
voltage data. Fig. 2 shows the resistance of the two ohmic contacts
after annealing from 220 C to 390 C for 30 s. In the n-type
ohmic contact system, the Cu/Ge/Pd (150 nm/150 nm/15 nm)
system shows the lowest contact resistance of 4.4 106 O cm2
at an annealing temperature of 250 C and the Cu/Pt/Ti/Pt
(150 nm/60 nm/50 nm/5 nm) system shows the lowest value of
6.9 106 O cm2 at an annealing temperature of 310 C. Both ohmic
contacts for n-GaAs and p-Ge showed a contact resistance value in
the range of 106 O cm2, low enough for a practical III–V device
application.