A thermodynamic approach to ohmic contact formation to p-GaN

A new ohmic contact scheme for gallium nitride is presented. The use of Nit ride-forming metal Over Gallide-forming metal, "NOG", can modify the thermo dynamic activity of N and Ga near the interface. This in rum can modify the near-surface point defect concentrations, particularly the vacancies of Ga and N. The principle of this contact scheme was shown to be consistent wit h results from Ni/Au, Ni/Zn-Au, Ta/Ti, and Ni/Mg/Ni/Si contacts. In the pre sent study, the "NOG" scheme was used to design Ni/Ti/Au and Ni/Al/Au metal lization, and addition of Ti and Al nitride-forming metals to the Ni gallid e-forming metal led to lower but still high contact resistance. Ti was show n to be better than Al as the nitride-forming metal based on the decrease o f resistance in as deposited contacts. Compared to Ni/Au, four times more c urrent was measured in Ni/Ti/Au contacts to p-GaN after anneal at 300 degre esC for 5min. However the addition of the Ti nitride-forming metal led to l ower stability at 500 degreesC.