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 8C) 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 8C . A minimum specific contact resistivity of 3 10 4 V cm 2 was obtained after annealing over a broad range of temperatures (800– 950 8C 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 8C. By 900 8C 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 8C.