Scandium-Based Ohmic Contacts to InAlN/GaN Heterostructures on Silicon

We report a novel Sc/Al/Ni/Au metal scheme for Ohmic contacts to InAlN/GaN HEMT structures on silicon. A contact resistance of 0.39 Ω-mm with a low surface roughness of 20± 3 nm of the annealed contact has been achieved using this metal scheme. The microstructure of the region under the contacts revealed the formation of ~60 nm deep ScGaN inclusions in the GaN channel layer. A thin (~3-5 nm) non-uniform layer of ScInAlN is observed on top of InAlN barrier. Field-emission is found to be the dominant conduction mechanism. Polarization mismatch arising due to the structural modifications is used to explain the possible mechanism related to Ohmic contact formation.