Thermal Stability of Nitride-Based Diffusion Barriers for Ohmic Contacts to n-GaN

Abstract

The use of TaN, TiN, and ZrN diffusion barriers for Ti/Al-based contacts on n-GaN (n � 3 · 10 17 cm -3 ) is reported. The annealing temperature (600– 1,000� C) dependence of the Ohmic contact characteristics using a Ti/Al/X/Ti/Au metallization scheme, where X is TaN, TiN, or ZrN, deposited by sputtering was investigated by contact resistance measurements and Auger electron spectroscopy (AES). The as-deposited contacts were rectifying and transitioned to Ohmic behavior for annealing at ‡600� C. A minimum specific contact resistivity of � 6 · 10 -5 X-cm -2 was obtained after annealing over a broad range of temperatures (600–900� C for 60 s), comparable to that achieved using a conventional Ti/Al/Pt/Au scheme on the same samples. The contact morphology became considerably rougher at the high end of the annealing range. The long-term reliability of the contacts at 350� C was examined; each contact structure showed an increase in contact resistance by a factor of three to four over 24 days at 350� C in air. AES profiling showed that the aging had little effect on the contact structure of the nitride stacks.