Dependence of electrical properties on work functions of metals contacting to p-type GaN

The effects of GaN surface treatments and work functions of the contact metals on the electrical properties at the p-GaN/metal interfaces were investigated. A contamination layer consisting of GaO, and adsorbed carbons was found on the GaN substrate grown by metalorganic chemical vapor deposition. Most of the contamination layer was removed by annealing the Ni and Ta contacts at temperatures close to 5CKYC, resulting in slight increase of the current injection from the contact metal to the GaN. The resistance at the p-GaN/metal interfaces decreased exponentially with increasing the metal work functions, indicating that the Schottky barrier heights were sensitive to the metal work functions. The present study concluded that the contact metal with the large work function should be chosen to obtain for the non-reacted (non-alloyed) ohmic contacts to the p-GaN. However, non-reacted ohmic contacts to the p-GaN did not provide the low contact resistance required for blue laser diodes.