INVESTIGATION OF THE DEPENDENCE OF THE CONTACT RESISTANCE ON THE EXTERNAL GOLD LAYER IN AUNIGEAU/N-GAAS

The contact resistance of an Au/Ni/Ge/Au metallization system on n-GaAs exhibits a drop in contact resistance from 13.3 x 10(- 6) OMEGA-cm2 to 8.6 x 10(-6) OMEGA-cm2 when the external gold layer is varied from 800 angstrom to 6000 angstrom in thickness. Secondary ion mass spectroscopy indicates that the improvement in contact resistance is due to the gold's "regulating" the amount of NiAs formed, leading to an increase in the area fraction covered by the Ni2GeAs. The result shows that the external gold layer deposited to improve bonding should be optimized in thickness. This role played by the external gold layer of the metal system in affecting the contact resistance has not been previously studied.