Thermally stable Ti/Al-based ohmic contacts to N-polar n-GaN by using an indium interlayer

The electrical properties of In/Ti/Al/Au contacts to N-polar n-GaN (nd = 5×1018cm%3) for high-power vertical light-emitting diodes were investigated at various thicknesses of the In layer, and compared with those of Ti/Al/Au contacts. Before annealing, both the Ti/Al/Au and In/Ti/Al/Au contacts were ohmic. After annealing at 300 C for 1 min, all of the samples exhibited some degradation of their electrical properties, although the In/Ti/Al/Au samples were more thermally stable. After annealing at 300 C for 60 min, the Ti/Al/Au contacts became non-ohmic, while the In (5 nm)/Ti/Al/Au contacts remained ohmic with a contact resistivity of 2.6×10%4?cm2. X-ray photoemission spectroscopy (XPS) results showed that, for all of the samples, annealing caused an increase in the content of interfacial oxygen. Based on the XPS and electrical results, the annealing dependence of the electrical characteristics of In/Ti/Al/Au contacts are described and discussed.