Ohmic contacts with different metal structures for lattice matched InP based heterostructures

AuGeNiAu and PdGeAu contacts to InP based high electron mobility transistor (HEMT) structures are examined. Standard, non-recessed, transmission line model (TLM) structures do not accurately represent contact resistance when there is high interfacial resistance between InGaAs and InAlAs. A mathematical model using distributed resistance is reviewed. Three new TLM structures derived from the model are shown and new methods for measuring contact resistance are given. Different metal schemes were evaluated and different layer thicknesses within a given metal scheme were also compared using statistically designed experiments. PdGeAu was found to be consistently better for ohmic contacts than AuGeNiAu. The optimum thicknesses found in the PdGeAu system were 150/spl Aring/ of Pd and 500/spl Aring/ of Ge.<
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