Ohmic contact and interfacial reaction of Ti/Al/Pt/Au metallic multi-layers on n-Al_xGa_(1-x)N/GaN heterostructures

摘要

The specific contact resistivity (ρ_c) and interfacial reaction between Au/Pt/Al/Ti metallic multi-layers and Si-doped n-type Al_xGa_(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 x 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 ℃. 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_2N phase is formed at the interface after the sample is annealed at 800 ℃. In this case, the ρ_c further decreases.