Electrical and microstructural analyses on the Au/Ni/Au/Ge/Pd ohmic contact to n-InGaAs and n-GaAs

The Au/Ni/Au/Ge/Pd ohmic contact systems on n-InGaAs and n-GaAs were studied and compared. In the contact to n-InGaAs, relatively good ohmic behavior was found even without annealing due to lower barrier height, and a better ohmic contact was obtained by rapid thermal annealing up to 400 degrees C. However, above 425 degrees C it was deteriorated by intermixing and phase reaction of the ohmic metals and InGaAs substrate. The out-diffusion of In and As degraded the ohmic contact due to an increase in barrier height and charge compensation. As for the contact to n-GaAs, non-ohmic behavior was shown before annealing, but significant reduction of the specific contact resistance was made by annealing. In both contacts, non-spiking and planar interfaces were observed even when annealed at 425 degrees C, and surface morphologies were nearly the same as the as-deposited contacts up to 400 degrees C, which showed smooth and shiny surfaces.