Structural and electrical characterization of AuPdAlTi ohmic contacts to $AlGaN∕GaN$ with varying Ti content Available to Purchase

$AuPdAlTi∕AlGaN∕GaN$ ohmic contact structures with varying Ti:Al ratios have been investigated. The relationship between Ti:Al ratio, interfacial microstructure, and contact resistance is examined. Rapid thermal annealing temperatures of $850°C$ or higher are required to produce an ohmic contact with annealing at $950°C$ producing the lowest contact resistance in the majority of samples. Samples annealed at $950°C$ have been analyzed using complementary transmission electron microscopy and electrical characterization techniques. A thin Ti-nitride region is found to form at the contact/semiconductor interface in all samples. Ti-nitride inclusions through the $AlGaN∕GaN$ layer are also observed, surrounded by an $Al∕Au$ rich metallurgical barrier layer, with the size of the inclusions increasing with Ti content. The size of these inclusions does not have any clear effect on the electrical characteristics of the contacts at room temperature, but samples with fewer inclusions show superior electrical characteristics at high temperatures.