New models for ohmic contacts to GaAs

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Department of Electrical and Computer Engineering


Gold-based ohmic contacts are routinely used in GaAs devices and integrated circuits. Since either electron-beam deposited or thermally evaporated gold is in the polycrystalline form, grain boundary diffusion of gallium into gold is expected. Using sputter Auger depth profiles of electron-beam deposited and annealed gold contacts on n-type GaAs, the concentration of gallium in gold as a function of the annealing temperature (250 to 550 °C with a step of 50 °C) is determined. Applying Whipple's grain boundary diffusion theory, the grain boundary diffusion coefficient for gallium in gold layer is found to be 3.5 × 10-9 exp(-0.21/kT) cm2s-1. The lattice diffusivity is equal to 6.5 × 10-13 exp(-0.33/kT) cm> 2s-1. The study on gold diffusion in GaAs based on the capture of gold atoms by gallium vacancies and gold migration along interstices yielded the diffusion coefficient of gold equal to 3.12 × 10-3 exp(-1.59/kT) cm2 s-1.

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Thin Solid Films