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(11)//GaN(0002)
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.
© 1999 American Institute of Physics.