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

• Published in: Journal of applied physics 2004-11, Vol.96 (10), p.5588-5595
• Main Authors: Fay, M. W., Moldovan, G., Weston, N. J., Brown, P. D., Harrison, I., Hilton, K. P., Masterton, A., Wallis, D., Balmer, R. S., Uren, M. J., Martin, T.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1796514

Au Pd Al Ti ∕ Al Ga N ∕ Ga N 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.