In this paper, Au-Ge/Pt/Au ohmic contact to n-type GaAs with 5nm thickness of Pt first layer was effective in reducing the dependency of annealing temperature. The specific contact resistance was $2.3×10^{-4}~6.1×10^{-4}Ω㎠$ at the temperature range of 350~450℃. Pt first layer was effective not only in suppressing out-diffusion of Ga and As but also in reducing the alloying depth of GaAs substrate with contact metals. From these reasons, it was thought that interface morphology of the metal/GaAs and surface morphology were improved. X-ray diffraction, atomic force microscopy, scanning electron microscopy, transmission electron microscopy and Auger electron spectroscopy were utilized.
