Metallurgical Interactions at the Contacts GaAs Interface

摘要

Interface morphology, phase composition, and elemental diffusion of Pt/Ti/Ge/Pd ohmic contacts to both n and p~+-GaAs have been investigated as a function of annealing temperature. Structural and chemical results were correlated with specific contact resistances (ρ_c) measured for each thermal treatment. Annealing at 450℃ yielded the lowest ρ_c, ～6.4 x 10~(-7)Ω-cm~2. The interface was observed to be smooth and abrupt. Two interface phases were detected; a primary phase, PdGe, and a secondary, Ga-rich Pd-Ga-As ternary phase. The presence of this ternary phase was found to be critical to contact formation on n-GaAs. The Ti and Pt layers remained pristine. Annealing at 550℃ resulted in a slightly higher ρ_c, ～2.1 x 10~(-6)Ω-cm~2. There was significant elemental diffusion within the contact metal and minor diffusion into the GaAs substrate. The interface possessed limited areas of spiking with uniform composition. Annealing at 600°C proved to have a detrimental effect on the ρ_c, ～10~(-4)Ω-cm~2. This electrical degradation was accompanied by strong chemical intermixing between the contact and substrate, resulting in a continuous nonplanar interface with deep multiphase protrusions.