The Alloying of Gold and Gold Alloy Ohmic Contact Metallizations with Gallium Arsenide

Abstract

The al loying of gal l ium arsenide with thin films of pure gold and the gold 12 % germanium-s i lver-go ld hmic contact metal l izat ion used for a GaAs FET, has been invest igated using optical and scanning electron microscopy. The heating rate and max imum temperature attained during heat- t reatment was found to govern the morphology of the pure gold films, and to a lesser extent the ohmic contact metall izations. The al loying cycle commences with decom-posit ion of the under ly ing GaAs and diffusion of gal l ium into the metal at about 260 ~ Melting commences above about 480 ~ with pure gold and 360~ with the contact metall ization. The final gal l ium content of the metal increases as the temperature is increased and the solidification temperature of both a pure gold and mult icomponent contact heated to 525 ~ is 343 ~ • 2 ~ The GaAs-meta l interface is very i r regular consisting of approximately rectangular depressions, often over 1 #m deep, filled with metal. Gold is used extensively in the fabrication of gal l ium