Use of TiB2 diffusion barriers for Ni/Au ohmic contacts on p-GaN

The use of a TiB2 diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25-950 °C) dependence of ohmic contact characteristics using a Ni/Au/TiB2/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500 °C . A minimum specific contact resistivity of ∼3 × 10−4 Ω cm−2 was obtained after annealing over a broad range of temperatures (800-950 °C for 60 s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB2 at 800 °C. By 900 °C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB2 diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500 °C.