Preparation of non-alloyed metal contacts to n-type gallium nitride with ultralow specific contact resistivity of 5.8 × 10−9 Ω cm2

A fabrication process for non-alloyed metal contacts to n-type gallium nitride (GaN) is presented. Following pulse sputtering deposition of GaN doped with high-concentration germanium, ultra-high vacuum evaporation of various metals was performed, achieving a contact resistivity on the order of 10−9 Ω cm2. The contact resistivity decreased monotonically with increasing electron concentration in the degenerate doping regime of GaN, confirming the predominance of tunneling transport. The observed differences in contact resistivity among metals cannot be explained solely by work function variations, suggesting that interfacial reactions and/or defect generation at the metal/GaN interface play significant roles. The contact resistivity of 5.8 × 10−9 Ω cm2 obtained with vanadium represents, to the best of our knowledge, the lowest value reported to date for non-alloyed contacts to n-type GaN. These results identify vanadium as a promising contact metal for high-power electro-optical GaN devices.