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 was investigated.,The: minimum specific contact resistance (Q(c)) obtained was 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-type GaN was examined with transmission electron microscope (TEM) in conjunction with compositional analyses. The high value of Q(c) for samples heat treated at lower temperatures (< 400 degrees C) was attributed to the fact that Au islands and crystalline NiO detached from the p-type GaN. When the temperature increased to 500 degrees C, NiO films and Au islands epitaxially constructed on p-type GaN matrix. The crystalline NiO may play a crucial role in the formation of low-resistance ohmic contact to p-GaN. Increasing the 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.