Realization of low specific-contact-resistance on N-polar GaN surface using heavily-Ge-doped n-type GaN films deposited by low-temperature reactive sputtering technique

Abstract We developed a low-temperature ohmic contact formation process for N-polar GaN surfaces. Specific-contact-resistances of 9.4 × 10 −5 and 2.0 × 10 −5 Ω·cm 2 were obtained using Ti/Al metal stacks on heavily-germanium-doped GaN films, which were deposited at 500 °C and 600 °C using a radical-assisted reactive sputtering method, respectively. The electrode sintering temperature was as low as 475 °C. Carrier concentrations for the 500 °C and 600 °C samples were 2.6 × 10 20 and 1.8 × 10 20 cm −3 , respectively. These results suggest that this method is highly effective in reducing the contact resistance of GaN devices with low thermal budgets.