Low Thermal Budget Au-Free Hf-Based Ohmic Contacts on InAlN/GaN Heterostructures

Abstract

We report Au-free Hf/Al/Ta ohmic contacts on InAlN/GaN-on-Si with low contact resistance (Rc) of 0.59 Ω.mm and contact resistivity (ρc) of 6.7×10-6 Ω.cm2 achieved using a low annealing temperature (600 oC). The dominant carrier transport mechanism is found to be electron thermionic field emission, as revealed by current-voltage-temperature measurements. Hf/Al/Ta ohmic contacts possess good surface morphology and edge acuity, and have a smooth interface with InAlN/GaN. Based on SIMS studies, formation of HfN is believed to be the reason for the formation of ohmic contacts. Preliminary thermal aging test shows that Hf/Al/Ta contacts on InAlN/GaN are stable at 350 oC in air for more than 200 hours.