Interdiffusions in thin-film Au on Pt on GaAs (100) studied with Auger spectroscopy

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Abstract
It has been proposed that interdiffusion of Pt, Au, and GaAs constitutes one major source of instability in GaAs microwave devices with Pt/Au metallization. In order to determine the extent of interdiffusion of these materials, preparations of Pt/GaAs and Au/Pt/GaAs were heat treated over the range 250–500 °C, and chemical depth profiles were obtained by measuring the surface composition with Auger electron spectroscopy while ion milling. Platinum films were 125–9000 Å thick. When Pt/GaAs was heated in vacuum, the Pt‐GaAs interaction initiated with a rapid migration of Ga into Pt and simultaneous formation of an As‐rich layer at the Pt/GaAs interface. Gallium eventually traveled the entire thickness of even the 9000‐Å Pt film while arsenic stopped abruptly at a distance ∼2/3 of the way into the Pt. Little or no Au was detected (heated in air behaved similarly with two added features: a surface layer containing mostly Ga and O formed over the Pt, and oxygen diffused through the (reacted) Pt to form an oxygen‐rich layer at the Pt/GaAs interface. Interdiffusion (during air anneal) was found to be reduced when the GaAs was oxidized prior to Pt deposition.