Nb-Ti/Al/Ni/Au based ohmic contacts to AlGaN/GaN

In this paper, we report on a novel Nb-Ti/Al/Ni/Au metallic system proposed to form ohmic contact to AlGaN/GaN heterostructure. The metallic system uses deposition of thin niobium layer as the first layer in contact with the AlGaN barrier layer before deposition of the conventional Ti/Al/Ni/Au metallic system. The fabrication and electrical characterization of the Nb-Ti/Al/Ni/Au based ohmic contacts are presented. We have shown that Nb-based ohmic contacts at optimal alloying temperatures seem to be superior to that of conventional Ti/Al/Ni/Au in both surface morphology and contact resistivity evaluation. Auger Electron Spectroscopy (AES) and Secondary Ion Mass Spectroscopy (SIMS) are also used to evaluate the improved ohmic contact formation.