Ohmic contact and interfacial reaction of Ti/Al/Pt/Au metallic multi-layers on n-AlxGa1−xN/GaN heterostructures

The specific contact resistivity (ρ C ) and interfacial reaction between Au/Pt/Al/Ti metallic multi-layers and Si-doped n-type Al x Ga 1-x N (n-AlGaN) layers in modulation-doped Al 0.22 Ga 0.78 N/GaN heterostructures have been investigated. By means of the measurements based on the transmission line model, the ρ C as low as 1.6 × 10 -4 Ωcm 2 is obtained. Based on the X-ray diffraction analysis, it is found that N atoms in n-AlGaN layer diffuse out and a much amounts of N-vacancies are formed in n-AlGaN layer near the interface after the sample is annealed at temperatures higher than 500 °C. It induces the heavy n-type doped region in n-AlGaN near the interface, and thus leads to the decrease of the ρ C . With increasing the annealing temperature, more N atoms in n-AlGaN layer diffuse out and react with Ti atoms. Ti 2 N phase is formed at the interface after the sample is annealed at 800 °C. In this case, the ρ C further decreases.