Auger depth profile analysis and EFTEM analysis of annealed Ti/Al-contacts on Si-doped GaN

Ti/Al (10 nm/100 nm) bilayer contacts on Si-doped GaN were heat treated for 30 s at 600 and 650°C. The microstructure of the contacts was analysed by Auger depth profiling, SEM and EDX analysis and energy filtering TEM using electron spectroscopic imaging (ESI). The experiments show a strong interdiffusion of Al and Ti leading to the formation of an intermetallic compound. A complex, spatially inhomogeneous structure consisting of an Al-rich phase, a Ti–Al intermetallic compound and regions containing Al-oxide is formed, while the GaN is still covered by a thin, homogeneous Ti-rich layer. A thickness of 2.5 nm was obtained for the Ti-rich layer in the contact heat treated at 650°C. The combination of complementary results from Auger depth profiling, SEM analysis with EDX and ESI provides a comprehensive characterisation of the complex contact structure. The results will be discussed in terms of the contributions and specific advantages of the individual techniques.