In the last decade, Pd-Ge contact system emerged as the most promising replacement of the Au-Ni-Ge alloy, still used by most of today's GaAs technology. Its better electrical properties stem from the fact that contact formation is based on a series of solid state reactions without any melting of the metal thin films and the GaAs substrate taking place during annealing. Research studies by E.D. Marshall et al. (1) demonstrated that thermally stable contacts with low resistivities could be achieved by low temperature annealing of Pd and Ge thin films. Their studies also revealed that the excess Ge is regrown on top of the GaAs substrate by a solid state epitaxy mechanism.

Typical TEM cross-sectional specimen preparation techniques limit the electron transparent area and make the global characterization of the contact difficult. In this study, we employed a focus ion beam (FEB) method as described by Bassile et al.(2), which allowed us to observe a minimum of 4 microns of the interface cross section in each of the specimens examined.