Thermally stable TiB ₂ Ohmic contacts on n-ZnO

The annealing temperature dependence of contact characteristics on bulk single-crystal n-ZnO using a TiB ₂/Pt/Au metallization scheme deposited by sputtering are reported. The contacts are rectifying for anneal temperatures <700°C but transition to Ohmic behavior at higher temperatures and exhibit a minimum specific contact resistivity of 5 × 10 ^-4 Ω cm after 800°C anneals. Higher temperatures lead to severe contact metallurgy intermixing and a sharp increase in specific contact resistivity associated with an increase in sheet resistance of the ZnO under the contact. Pt, Ti, Zn, and B outdiffuse through the Au layer at 800°C while at higher temperatures the contact morphology is destroyed. These boride-based contacts show much higher thermal stability than previous metal schemes used as Ohmic contacts on ZnO and are promising for high-temperature device applications.