Synchrotron radiation X-ray photoelectron spectroscopy study of interface reactions in Al/Ti/GaN ohmic contacts

Nozaki, Mikito*; Ito, Joyo*; Asahara, Ryohei*; Nakazawa, Satoshi*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka ; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Interface reactions between Ti-based multilayer electrodes on n-type GaN epilayers were investigated by means of synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS). High-resolution SR-XPS analysis revealed formation of metallic Ga and TiN mixed interlayers at Ti/GaN interface even at room temperature by depositing Al capping layer. By comparing XPS spectra from the stacked Al/Ti electrode and single Ti electrode, an essential role of Al overlayers serving as oxygen diffusion barrier and oxygen scavenging element to produce reactive pure Ti underlayers on GaN was demonstrated. Moreover, growth of metallic interlayers consisting of Ga and Ti atoms during vacuum annealing was clearly identified from in situ SR-XPS analysis.