The effect of thermal annealing on the Ni/Au contact of p-type GaN

In this study, the Ni/Au layers prepared by electron beam evaporation and thermal alloying were used to form Ohmic contacts on $\mathrm{p-}$ type GaN films. Before thermal alloying, the current–voltage $\mathrm{(I–V)}$ characteristic of Ni/Au contact on $\mathrm{p-}$ type GaN film shows non-Ohmic behavior. As the alloying temperature increases to 700 °C, the $\mathrm{I–V}$ curve shows a characteristic of Ohmic contact. The Schottky barrier height reduction may be attributed to the presence of Ga–Ni and Ga–Au compounds, such as ${\mathrm{Ga}}_{\mathrm{4}}{\mathrm{Ni}}_{\mathrm{3}}{\mathrm{,\hspace{0.5em}Ga}}_{\mathrm{3}}{\mathrm{Ni}}_{\mathrm{2}}\mathrm{,}$ GaAu, and ${\mathrm{GaAu}}_{\mathrm{2}},$ at the metal-semiconductor interface. The diffusing behavior of both Ni and Au have been studied by using Auger electron spectroscopy and Rutherford backscattering spectrometry. In addition, x-ray diffraction measurements indicate that the ${\mathrm{Ni}}_{\mathrm{3}}\mathrm{N}$ and ${\mathrm{Ga}}_{\mathrm{4}}{\mathrm{Ni}}_{\mathrm{3}}$ compounds were formed at the metal-semiconductor interface.