A study of the Au/Ni ohmic contact on p-GaN

The formation mechanism of the ohmic Au/Ni/p-GaN contact has been investiga ted. We found that it is essential to (i) deposit a structure of Au and Ni in the proper deposition sequence, and (ii) anneal the bilayer structure in an oxygen containing ambient. Our findings indicated that oxygen assists t he layer-reversal reactions of the metallized layers to form a structure of NiO/Au/p-GaN. The presence of oxygen during annealing appears to increase the conductivity of the p-GaN. It is further suggested that Ni removes or r educes the surface contamination of the GaN sample before or during layer r eversal. In the final contact structure, an Au layer, which has a large wor k function, is in contact with the p-GaN substrate. The presence of Au in t he entire contacting layer improves the conductivity of the contact. An ohm ic formation mechanism based on our experimental results is proposed and di scussed in this work. (C) 2000 American Institute of Physics. [S0021-8979(0 0)02621-9].