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

Abstract

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 cm2) was realized successfully.

Direct Writing of Functional Layer by Selective Laser Sintering of Nanoparticles for Emerging Applications: A Review

“…Among non-noble metals, copper (Cu) [ 15 , 43 ] receives special attention due to its high electrical conductivity compared to that of noble metals, together with superior cost-effectiveness. A critical issue, however, is that Cu is easily oxidized in ambient conditions.…”

Copper inks for printed electronics: a review

“…Thus, to realize sintering at lower temperatures (<120 °C) and solve the oxidation problem, copper-based inks with different formulations have been developed in previous research works. [74][75][76][77][78][79] The different types of ink materials can be classified as follows: copper particle ink, copper nanowire ink, copper precursor ink, and copper mixed ink. This section discusses different formulations of copper inks and their performance.…”

1,8‐Octanedithiol as an Effective Intermediate Layer for Deposition of Cu Electrodes via Inkjet Printing and Laser Sintering on III–V Triple‐Junction Solar Cells

“…In general, the thickness of deposited conductive thin films considerably influences their electrical contact behavior. [ 6,56 ] However, deposited films with a thickness in the nm range may have higher resistivity than bulk Cu due to the porosity, the dependence of carrier mobility on crystallinity, and materials’ nanostructure. [ 57–59 ]…”

“…However, fluence values higher than this optimized value lead to ablation of the ink resulting in a nonohmic electrical contact. [ 6 ]…”

“…[ 6 ] Recently, they have been applied considerably as electrode materials for various electronics (e.g., solar cells) due to their low production cost compared with silver or other noble metals. [ 6–12 ]…”