Ohmic Contacts on N-Face n-Type GaN After Low Temperature Annealing

The electrical properties of different metal systems for ohmic contacts on the nitrogen-face of c-plane n-type GaN substrates are investigated. The metal contacts are compatible with the fabrication process and the packaging technology for group III-nitride laser diodes. The metal system Ti/Al/Mo/Ti/Ni/Au/Ti/Pt is determined as the best suitable, since it is ohmic already after annealing at a temperature of 450°C for 60 s. This annealing temperature is high enough to make the contact insensitive against later soldering on a heat-sink at 330°C. At the same time, the temperature is low enough that the Pd-based p-contact, previously annealed at 530°C, does not degrade. In addition, the Ti/W/Al and Pd/Ti/Al metal systems form low-resistance ohmic contacts, too, although they require a longer annealing time of several minutes or a higher temperature of 500°C.