SHALLOW OHMIC CONTACT FORMATION BY SEQUENTIAL DEPOSITION OF PD/AUGE/AG/AU ON GAAS AND RAPID THERMAL ANNEALING

Shallow ohmic contacts to n-GaAs are fabricated by sequential deposition of Pd/AuGe/Ag/Au and rapid thermal annealing at 450-500-degrees-C for 30 s. The metallization displays good electrical properties with a contact resistivity of 2 X 10(-6) OMEGA cm2. The film-substrate reaction is extremely limited and the interface is uniform. A systematic study of various AuGe metallization schemes indicates that the limited interfacial reaction observed in the Pd/AuGe/Ag/Au structure correlates with the stability of Au-Ag solid solutions against GaAs. The diffusion of silver into the AuGe layer upon heating increases the eutectic temperature of the system. As a result, the contact stays in a solid state when the metallurgical reaction takes place to form an ohmic contact.