The effects of germanium concentration on the compound formation and morphology of gold-based contacts to gallium arsenide

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Abstract
Alloyed Au–Ge thin films on n-GaAs are widely used for fabricating Ohmic contacts to n-type GaAs. This paper presents a systematic study of the effects of Ge concentration on the compound formation and morphology in the metallization. The lowest annealing temperature at which the compound formation at 10−6 Torr was observed for Au–Ge contacts with Ge concentrations of 0, ∼0.6, 3, and 12 wt. % Ge was 500, 500, 450, and 350 °C, respectively. Hence, Ge was found to decrease the compound formation temperature. Au7Ga2 was observed in contacts with low Ge concentrations (0 and ∼0.6 wt. % Ge), whereas α′-AuGa (or Au7Ga), a tentatively identified Au3Ga phase, and a AuGeAs ternary phase were observed in contacts with a Ge concentration of 12 wt. %. At an intermediate Ge concentration (3 wt. % Ge), both Au7Ga2 and α′-AuGa were observed. The morphology after compound formation was sensitive to the Ge concentration. In Au–Ge contacts, a change in the Ge concentration from 0 to ∼0.6 wt. % caused a sharp decrease in the aspect ratio of the aligned Au7Ga2 rectangular particles; a change from 3 to 12 wt. % Ge caused a change from a GaAs-rich matrix to a Au-rich matrix with the appearance of characteristically shaped AuGeAs patches.

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