In situ X-ray diffraction study of the effects of germanium and nickel concentrations on melting in gold-based contacts to gallium arsenide

Using X-ray diffraction in situ at 1 atm, the melting of the as-deposited film and the formation of the reaction product was investigated for gold, Au-Ge and Au-Ge-Ni contacts with various germanium and nickel concentrations. For the Au-Ge contact, the melting temperature of the as-deposited film was found to be 512±12 °C, 486±13 °C, 363±12 °C, and 363±12 °C with germanium concentrations of 0 wt.%, about 0.6 wt.%, 3 wt.% and 12 wt.% respectively. For the Au-Ge-Ni contacts, the melting temperature of the as-deposited film was 363±12 °C, 363±12 °C and 413±11 °C with germanium concentrations in the range 10-12 wt.% and nickel concentrations of 0 wt.%, 4 wt.% and 17 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₇Ga₂ formed in Au-Ge contacts with 0-3 wt.% Ge and it melted on second heating at 405±5 °C, 387±18 °C and 337±12 °C for germanium concentrations of 0 wt.%, about 0.6 wt.% and 3 wt.% respectively. On subsequent cooling after the melting of the contact film, Au₂Ga formed in Au-Ge contacts with 12 wt.% Ge and Au-Ge-Ni contacts; Au₂Ga melted on second heating at 363±12 °C for Au-Ge-Ni contacts with 12 wt.% Ge and 4 wt.% Ni, and at 413±11 °C for Au-Ge-Ni contacts with 10 wt.% Ge and 17 wt.% Ni. Hence germanium decreased the melting temperatures of α-AuGa (gold-rich solid solution) and Au₇Ga₂ because of the presence of dissolved germanium in these phases. In addition, nickel increased the melting temperature of α-AuGa (gold-rich solid solution) and Au₂Ga owing to the presence of dissolved nickel in these phases.