The effect of heat treatment on Ni/Au ohmic contacts to p-type GaN

The effect of heat treatment temperature on the microstructure and specific contact resistance of oxidized Ni(5 nm)/Au(5 nm) contacts to p-type GaN wa s investigated.,The: minimum specific contact resistance (Q(c)) obtained wa s 4 x 10(-6) Omega cm(2) after heat treating at 500 degrees C in air for 10 min. The cross-sectional microstructure of heat treated Ni/Au films on p-t ype GaN was examined with transmission electron microscope (TEM) in conjunc tion with compositional analyses. The high value of Q(c) for samples heat t reated at lower temperatures (< 400 degrees C) was attributed to the fact t hat Au islands and crystalline NiO detached from the p-type GaN. When the t emperature increased to 500 degrees C, NiO films and Au islands epitaxially constructed on p-type GaN matrix. The crystalline NiO may play a crucial r ole in the formation of low-resistance ohmic contact to p-GaN. Increasing t he temperature further to 600 degrees C, large voids adjacent to p-GaN were observed which resulted in the reduction of contacting area deteriorating the contact resistance.