Interfacial reactions between nickel thin films and GaN

Thin Ni films on GaN were annealed at temperatures between 400 and 900°C in N₂, Ar, and forming gas and were analyzed using glancing angle x-ray diffraction and Auger depth profiling. The first indication of an interfacial reaction was found after an anneal at 600°C for 1 h, after which Ga was observed to be dissolved in the face-centered cubic Ni film. The extent of dissolution increased with continued annealing. After annealing at 750°C for 1 hr in either N₂ or Ar, greater intermixing occurred. The reaction product was either Ni₃Ga or face-centered cubic Ni with dissolved Ga. Annealing at 900°C resulted in the formation of the B2 phase NiGa. It was clear from Auger depth profiles that the reacted film contained significantly more Ga than N and that N₂ gas 1 was released to the annealing environment, even when the samples were annealed in N₂ gas at 1 atm. Thus, a trend of increasing Ga content in the reacted films was observed with increasing temperature. The observed reactions are consistent with the thermodynamics of the Ni-Ga-N system.