For the past decade, there has been considerable focus on low resistance Pd-Ge ohmic contacts to GaAs. One approach toward achieving thermodynamically stable ohmic contacts is to consider solid-phasereactions for contacts, rather than the liquid phase interactions that occur upon ohmic alloying of Au-Ge-based systems. The two classifications to this approach are: low temperature annealing (<500°C), mainly using Pd, and high temperature annealing (<500°C), mainly using In. The low temperature annealing class is more compatible with existing GaAs technology, hence the attention to Pd-based systems, particularly Pd-Ge. There has also been tremendous interest in hybrid GaAs-on-Si technology. As an alternative to direct lattice-mismatched growth of GaAs on Si, the epitaxial lift-off (ELO) technique has been used, wherein GaAs devices grown on GaAs substrates can be removed and bonded to any substrate regardless of orientation and/or lattice matching criteria. This process yields high quality dislocation-free GaAs-based devices for hybrid applications.In this study, we demonstrate a low resistance non-alloyed Pd-Ge ohmic contact to epitaxialiy lifted-off n-type GaAs.
Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN
