AU GE NI OHMIC CONTACTS TO N-TYPE INP

The relationship between the electrical properties and microstructure for annealed Au/Ge/Ni contacts to n-type InP, with an initial doping l evel of 10(17) cm-3, have been studied. Metal layers were deposited by electron beam evaporation in the following sequence: 25 nm Ni, 50 nm Ge, and 40 nm Au. Annealing was done in a nitrogen atmosphere at 250-4 00-degrees-C. The onset of ohmic behavior at 325-degrees-C corresponde d to the decomposition of a ternary Ni-In-P phase at the InP surface a nd the subsequent formation of Ni2P plus Au10In3, producing a lower ba rrier height at the InP interface. This reaction was driven by the inw ard diffusion of Au and outward diffusion of In. Further annealing, up to 400-degrees-C, resulted in a decrease in contact resistance, which corresponded to the formation of NiP and Au9In4 from Ni2P and Au10In3 , respectively, with some Ge doping of InP also likely. A minimum cont act resistance of 10(-7) OMEGA-cm2 was achieved with a 10 s anneal at 400-degrees-C.