Interfacial reactions between gold thin films and GaAs substrates

Abstract

Interfacial reactions between polycrystalline thin films of gold, either 30 or 60 nm in thickness, and monocrystalline substrates of GaAs have been investigated as a function of deposition temperature and subsequent annealing conditions by transmission electron microscopy, incorporating a special cross-sectioning technique. For depositions of gold onto GaAs{100} substrates at ambient temperature, interfacial reactions proceed in four separate stages during isothermal annealing at temperatures ranging between room temperature and 350 °C: (1) elongated pyramidal pits, bounded by GaAs{111} planes and the original AuGaAs{100} interface, form during annealing for 30 min at 100 °C; (2) precipitates of Au 2Ga form in GaAs near the AuGaAs interface during annealing for 30 min at 200 °C or during annealing for about 6 months at room temperature; (3) these precipitates redissolve during annealing for 30 min at 320 °C; (4) the remaining (unalloyed) gold agglomerates in monocrystalline form at the pyramidal pits by solid state surface diffusion during annealing for 30 min at 330 °C. The orientation relationships between the monocrystalline gold and GaAs are {111} Au // {111} GaAs and 〈211〉 Au // 〈110〉 GaAs . For depositions of gold onto {100} substrates of GaAs at 280 °C and subsequent annealing at 330 °C, pyramidal pits bounded by GaAs{111} planes and agglomerated monocrystalline gold form, containing a reaction product of a monocrystalline hexagonal AuGa phase. The orientation relationships between the monocrystalline gold, hexagonal AuGa phase and GaAs are {111} Au // {01 10} AuGa // {111} GaAs and 〈110〉 Au // 〈0001〉 Au Ga // 〈110〉 GaAs . The formation (and dissolution) of these phases, the resultant morphology and the corresponding orientation relationships are interpreted in terms of both thermodynamic and crystallographic concepts.