Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN

Li Chien Chen*, Fu Rong Chen, Ji Jung Kai, Li Chang, Jin Kuo Ho, Charng Shyang Jong, Chien C. Chiu, Chao Nien Huang, Chin Yuen Chen, Kwang Kuo Shih

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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The microstructure of oxidized Ni/Au films on p-GaN was examined to elucidate the formation of a low resistance ohmic contact to p-GaN with a field-emission gun transmission electron microscope in conjunction with composition analyses. The p-GaN/Ni/Au samples were heat treated at 500°C in air mainly composed of a mixture of crystalline NiO, Au, and amorphous Ni-Ga-O phases. Small voids adjacent to the p-GaN film were also observed. The as-deposited Au film converted into discontinuous islands containing small amounts of Ni that connect with p-GaN. NiO formed a continuous film at the surface that covers the Au islands and the amorphous Ni-Ga-O phases. Moreover, NiO partially contacts p-GaN as well as Au islands and the amorphous Ni-Ga-O phase. The orientation relationship of the crystalline NiO, Au-rich islands, and p -GaN film was identified as NiO(111)//Au(111)//GaN(0002) and NiO[110]//Au[110]//GaN[1120]. The results suggested that Ni atoms diffuse through the Au layer onto the surface and react with oxygen to form NiO, whereas Au atoms diffuse towards the inside to form a Au-Ni alloy. The microstructural examination indicated that the crystalline NiO and/or the amorphous Ni-Ga-O phases may significantly affect the low resistance ohmic contact to p-GaN.

Original languageEnglish
Pages (from-to)3826-3832
Number of pages7
JournalJournal of Applied Physics
Issue number7
StatePublished - 1 Oct 1999

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