Characterization of Au and Al segregation layer in post-annealed thin Ti/Al/Mo/Au Ohmic contacts to n-GaN

The post-annealed interfacial microstructures of thin Ti/Al/Mo/Au metallization on n-GaN were investigated using analytical transmission electron microscopy. A 5–20-nm-thick continuous TiN layer was observed to have been formed due to the reaction between Ti and GaN. A continuous Au and Al segregation with a narrow thickness occurring exactly at the TiN/GaN interface was identified. Detailed structure and composition of the segregation layer were characterized. It is noted that despite the presence of Au at the interfacial region, an excellent Ohmic contact resistance was obtained. It suggests that the segregation of Au at the semiconductor/metal interface does not necessarily have detrimental effects on contact performance.