Ir diffusion barriers in Ni/Au ohmic contacts to p-type CuCrO ₂

The use of Ir diffusion barriers in Ni/Au-based Ohmic contacts to p-type CuCrO ₂ layers was investigated. A specific contact resistance of ~5 × 10 ^-4 Ω cm ² was achieved after annealing at 500°C for the Ir-containing contacts, and the contacts were rectifying for lower anneal temperatures. In this case, the contact resistance was basically independent of the measurement temperature, indicating that tunneling is the dominant transport mechanism in the contacts. The morphology for the Ir-containing contacts was still smooth at 500°C although Auger electron spectroscopy depth profiling showed that some of the nickel had diffused to the surface and had oxidized. Contacts annealed at 800°C showed that some copper and most of the nickel had diffused to the surface and oxidized. The presence of the Ir diffusion barrier does increase the thermal stability of the contacts by 200°C compared to conventional Ni/Au contacts. By contrast, the use of other materials such as TaN, ZrN, and W ₂B ₅ as the diffusion barrier led to poorer thermal stability, with the contact resistance increasing sharply above 400°C.