Role of annealing conditions and surface treatment on ohmic contacts to p-GaN and p-Al0.1Ga0.9N/GaN superlattices

The effects of the initial Mg reactivation annealing temperature, surface cleaning treatments, and contact annealing conditions on the specific contact resistance of Ni/Au ohmic contacts on p-GaN are reported. The lowest contact resistances were obtained for 900 °C activation annealing and cleaning steps that reduced the native oxide thickness (i.e., KOH rinsing). Removal of this interfacial oxide reduced the barrier for hole transport, providing a contact resistance of 9×10−4 Ω cm2 for Ni/Au metallization annealed at 500 °C. The use of a ten period p-Al0.1Ga0.9N(Mg)/GaN(Mg) superlattice with individual layer thickness 50 Å led to a specific contact resistance of 9×10−5 Ω cm2 under the same conditions.