AN INITIAL INVESTIGATION OF THE MICROSTRUCTURE OF TI/PD/AU OHMIC CONTACT STRUCTURES FOR GAAS MICROWAVE DEVICES APPLICATIONS

A preliminary investigation of both as-deposited and annealed titanium (75 nm), palladium (75 nm), gold (400 nm), ohmic contacts to thin p+-GaAs layers, was carried out using a combination of transmission electron microscopy, energy dispersive x-ray analysis, secondary ion mass spectroscopy and electrical measurements. The annealed contacts showed limited interaction between the metallization and the semiconductor with a metal penetration depth of only 2 nm for a 4 minute anneal at 380-degrees-C. The contacts were found to remain layered after annealing. The layers consisted of a uniform upper layer of large alpha Au(Ga) grains, a central, non-uniform layer containing small Pd-rich grains and a lower uniform layer of almost pure Ti. Preliminary SIMS studies suggested Zn dopant outdiffusion from the epilayer into the metal layer and this may have important implications for the electrical properties of these contacts.