Ohmic contact formation for inkjet-printed nanoparticle copper inks on highly doped GaAs.

GaAs compound-based electronics attracted significant interest due to unique properties of GaAs like high electron mobility, high saturated electron velocity and low sensitivity to heat. However, GaAs compound-based electronics demand a significant decrease in their manufacturing costs to be a good competitor in the commercial markets. In this context, copper-based nanoparticle (NP) inks represent one of the most cost-effective metal inks as a proper candidate to be deposited as contact grids on GaAs. In addition, Inkjet-printing, as a low-cost back-end of the line process, is a flexible manufacturing method to deposit copper NP ink on GaAs. These printed copper NP structures need to be uncapped and fused via a sintering method in order to become conductive and form an ohmic contact with low contact resistivity. The main challenge for uncapping a copper-based NP ink is its rapid oxidation potential. Laser sintering, as a fast uncapping method for NPs, reduces the oxidation of uncapped copper. The critical point to combine these two well-known industrial methods of inkjet printing and laser sintering is to adjust the printing features and laser sintering power in a way that as much copper as possible is uncapped resulting in minimum contact resistivity and high conductivity. In this research, copper ink contact grids were deposited on n-doped GaAs by inkjet-printing. The printed copper ink was converted to a copper grid via applying the optimized settings of a picosecond laser. As a result, an ohmic copper on GaAs contact with a low contact resistivity (8 mΩ cm) was realized successfully.