Interfacial reaction of Ni/Pt/Au contact schemes to p-type GaN

Glancing angle X-ray diffraction and Auger electron spectroscopy have been used to investigate interfacial reactions between the Ni(20 nm)/Pt(30 nm)/Au(80 nm) contacts and p-GaN (p = 9.4×10¹⁶ cm^-3). The metallization schemes were annealed at temperatures ranging from 500 to 700 °C for 30 s in a flowing Ar atmosphere. The anneal of the sample at 500 °C resulted in ohmic behavior with a specific contact resistance of 2.1×10^-2Ωcm². However, the anneal at temperatures ≥600 °C led to the degradation of the ohmic property. It is shown that Ga-(Pt,Ni) phases such as Ga₃Pt₅ and Ga₄Ni₃ and a Pt-Ni solid solution are formed upon annealing at 500 °C, while in addition to the Ga₄Ni₃, new phases of GaAu₂ and GaAu are formed upon annealing at temperatures ≥600 °C. As for the Pt-Ni solid solution, the lattice parameter decreases significantly with increasing annealing temperatures. A qualitative explanation is given to describe why the characteristic of the contacts changed from ohmic to rectifying behavior with increasing temperature.