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 ${\text{9×10}}^{\text{−4}}\mathrm{ \Omega }{\mathrm{cm}}^{\mathrm{2}}$ for Ni/Au metallization annealed at 500 °C. The use of a ten period $\mathrm{p-}{\mathrm{Al}}_{\mathrm{0.1}}{\mathrm{Ga}}_{\mathrm{0.9}}\mathrm{N(Mg)/GaN(Mg)}$ superlattice with individual layer thickness 50 Å led to a specific contact resistance of ${\text{9×10}}^{\text{−5}}\mathrm{ \Omega }{\mathrm{cm}}^{\mathrm{2}}$ under the same conditions.