Low resistance ohmic contacts to n-GaN and n-AlGaN using NiAl

The intermetallic compound NiAl (50:50 at. %) has been shown to be a low-resistance ohmic contact to n-GaN and n-AlGaN. NiAl contacts on n-GaN ${\text{(n=2.5×10}}^{17} {\mathrm{cm}}^{\mathrm{-3}})$ had a specific contact resistance of ${\text{9.4×10}}^{\text{−6}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}$ upon annealing at 850 °C for 5 min. NiAl contacts annealed at 900 °C for 5 min in $\mathrm{n-}{\mathrm{Al}}_{\text{0.12}}{\mathrm{Ga}}_{\mathrm{0.88}}\mathrm{N}{\text{\hspace{0.05em}(n=2.4×10}}^{18} {\mathrm{cm}}^{\mathrm{-3}})$ and $\mathrm{n-}{\mathrm{Al}}_{\mathrm{0.18}}{\mathrm{Ga}}_{\mathrm{0.82}}\mathrm{N}{\text{\hspace{0.05em}(n=2.7×10}}^{18} {\mathrm{cm}}^{\mathrm{-3}})$ had specific contact resistances of ${\text{2.1×10}}^{\text{−5}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}$ and ${\text{4.7×10}}^{\text{−5}}\hspace{0.17em}{\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}},$ respectively. Additionally, these contacts were subjected to long-term annealing at 600 °C for 100 h. On n-GaN, the contact specific contact resistance degraded from ${\text{9.4×10}}^{\text{−6}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}$ to ${\text{5.3×10}}^{\text{−5}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}$ after the long-term anneal. Contacts to $\mathrm{n-}{\mathrm{Al}}_{\mathrm{0.18}}{\mathrm{Ga}}_{\mathrm{0.82}}\mathrm{N}$ showed only slight degradation with a change in contact resistance, from ${\text{4.7×10}}^{\text{−5}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}$ to ${\text{9.2×10}}^{\text{−5}} {\mathrm{\Omega \hspace{0.17em}cm}}^{\mathrm{2}}.$ These results demonstrate the NiAl has great promise as a stable, low-resistance contact, particularly to n-AlGaN used in high-temperature applications.