The electrical and microstructural properties of Au/Ti and Au/Pd/Ti contacts to p+-GaAs (C-doped, 5×1018cm−3) were investigated. Current-voltage measurements as a function of temperature showed that the Ohmicity of the Au/Ti contact improved upon annealing. However, the annealed binary contact featured Au spiking into the GaAs making it unsuitable for HBT applications. The addition of a Pd diffusion barrier layer between the Au and Ti metallisation layers prevented spiking, but resulted in a decrease in the Ohmicity of the contact.
For all the contact systems it was found that thermionic-field emission dominates the current transport mechanism across the metal-semiconductor interface between the temperature range 198K and 348K. The Au/Pd/Ti contact structure shows HBT potential, however higher epilayer doping levels will be required to produce satisfactory specific contact resistivities.