Ohmic contacts to n-GaAs with Germanide overlayers

This paper reports a sintered ohmic contact to n type GaAs. The ohmic contact formation occurs by simultaneous synthesis of molybdenum germanide as a contacting metallurgy and a shallow n⁺type region formed in GaAs by germanium diffusion. Contact resistances of low 10^-6ω.cm²can be obtained on ion implanted n type GaAs with surface layers of peak doping in the 10¹⁷cm^-3range. The contacts are formed at 750° C under arsenic overpressure. The contacts formed are smooth and uniform in morphology. The degradation under temperature and time stress is found to be pronounced above 350° C at times longer than 3 hours with contact resistances in the high 10^-5ω.cm²range after 14 hours. The system exhibits comparable contact resistance, smoother morphology and a better temperature stability than the commonly used alloyed AuGe system.