Al-Si-Ti Ohmic Contacts on N-Type Gallium Nitride
Ohmic contacts represent a major technological brick for the development of high power devices on Gallium Nitride. Al(200 nm) Ti(70 nm) metallization on n+-GaN, annealed at 650 °C, provides a “Specific Contact Resistivity” (SCR) in the range mid 10-5 Ω.cm², which is low enough for the main switching power applications. However, the Al-Ti metallic compound phases formed during the annealing step result from solid-solid reactions, which may lead to high stress and / or poor cohesion, possibly deleterious to contact reliability. In this work, we have investigated several configurations of Ti-Al-Si based contacts, aiming at favoring liquid-solid reactions and / or Si element diffusion, in order to get better SCR and / or morphology and cohesion of the metallic phase. Surprisingly, only contacts annealed at low temperature (450 °C) provide low contact SCR, comparable to that of Ti-Al only contact, but systematically higher.
Edouard V. Monakhov, Tamás Hornos and Bengt. G. Svensson
N. Thierry-Jebali et al., "Al-Si-Ti Ohmic Contacts on N-Type Gallium Nitride", Materials Science Forum, Vols. 679-680, pp. 812-815, 2011