Diffusion Barrier Layers for Ohmic Contacts to GaAs

Barrier layers have been used on top of Ni-Au-Ge alloyed and Pd-Ge ``non-alloyed'' ohmic contacts for GaAs MESFET integrated circuits. They prevent diffusion of subsequent interconnection layers and so maintain stable low resistance (0.05 ohm. mm) contacts. The assessment of these contact structures, both electrically and using AES and TEM, is presented. The results show that the barrier action is effective in producing uniform and reliable contacts and good yields of MSI high speed digital circuits.