Combinatorial optimization of Ti/Al/Ti/Au ohmic contacts to n-GaN

• Published in: Physica status solidi. C Vol. 2; no. 7; pp. 2551 - 2554
• Main Authors: Davydov, A.V., Motayed, A., Boettinger, W.J., Gates, R.S., Xue, Q. Z., Lee, H. C., Yoo, Y. K.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01.05.2005; WILEY‐VCH Verlag
• Subjects: 73.40.Cg; 73.61.Ey
• ISSN: 1610-1634; 1610-1642
• DOI: 10.1002/pssc.200461605

A combinatorial library of Ti/Al/Ti/Au metal contacts to n‐type GaN thin films was characterized electrically and microstructurally. Various Ti/Al/Ti/Au thicknesses were deposited by combinatorial ion‐beam sputtering (CIBS) on an n‐GaN/sapphire substrate followed by rapid‐thermal annealing (RTA) at 600 °C to 900 °C in argon for 30 s. The most Al‐rich metallization in the library, Ti(20nm)/Al(170nm)/Ti(5nm)/ Au(50nm), was found to have the smoothest surface morphology (rms roughness = 20 nm), while possessing an acceptably low contact resistivity (2.2 × 10–5 Ω cm2) after RTA at 750 °C. XRD analysis of this composition showed that, regardless of RTA temperature, the same two compounds, Al3Ti and Al2Au, were formed in the contact layer. For all other library elements, the interfacial phases in the metal layers were subject to continuous transformations as a function of RTA temperature. We surmise that these temperature‐dependent transformations inflicted the excessive surface roughness in the contacts. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)