Alloying behavior of Ni/Au-Ge films on GaAs

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Abstract
Alloying behavior of thin Ni/Au-Ge films deposited on a GaAs substrate is investigated by using a microprobe Auger spectrometer and an x-ray diffractometer. The deposited films react with the substrate above 300 °C to form alloys with complex multilayer structure in the 300–400 °C temperature range and alloys with microscopic grain structure above 450 °C. Uniform alloying, accompanied with a smooth interface, is observed and is ascribed to the high reactivity of Ni with GaAs under a solid-solid phase. However, when the sample is annealed in the solid-solid phase, Ni penetrates irregularly into the GaAs substrate, if the annealing duration is too long, causing poor Ohmicity. Rapid Ge moving to the substrate interface is observed at 400 °C and is closely related to the formation of a Ge-doped degenerate layer beneath the contact. The high reliability of the contract, which is obtained when annealed at 500 °C, is explained by the metallurgical stability of the grain structure. Based on the results of this study, some rules for III-V compound semiconductor contact fabrication are proposed.