Effects of oxygen plasma treatment on the formation of ohmic contacts to GaN and AlGaN

The effects of oxygen plasma treatment prior to metal contact deposition have been studied for both n‐ and p‐GaN, as well as n‐AlGaN. In n‐GaN, the as‐deposited Ti/Al contacts change from rectifying to ohmic, and further improvements are observed after rapid thermal annealing (RTA). A specific contact resistivity better than 10 –7 Ω cm 2 was obtained using a plasma treatment of 20 s at 30 W and 0.2 mbar, followed by RTA at 500 °C in argon. The I–V characteristics of the Ti/Al contacts degraded when plasma treatments were performed for a longer time and/or at increased plasma pressure. However, in contrast to n‐GaN, the electrical properties of the Ni/Au contacts to p‐GaN and Ti/Al contacts to n‐Al 0.15 Ga 0.85 N deteriorated following oxygen plasma treatment. X‐ray photoelectron spectroscopy (XPS) was used in order to help elucidate the mechanisms behind these effects. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)