A Thermodynamic Approach to Ohmic Contact Formation to p-GaN

A new ohmic contact scheme for gallium nitride is presented. The use of Nitrideforming metal Over Gallide-forming metal, “NOG”, can modify the thermodynamic activity of N and Ga near the interface. This in turn 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 with results from Ni/Au, Ni/Zn-Au, Ta/Ti, and Ni/Mg/Ni/Si contacts. In the present study, the “NOG” scheme was used to design Ni/Ti/Au and Ni/Al/Au metallization, and addition of Ti and Al nitride-forming metals to the Ni gallide-forming metal led to lower but still high contact resistance. Ti was shown to be better than Al as the nitride-forming metal based on the decrease of resistance in as deposited contacts. Compared to Ni/Au, four times more current was measured in Ni/Ti/Au contacts to p-GaN after anneal at 300C for 5min. However the addition of the Ti nitride-forming metal led to lower stability at 500C.