Thermal stability of W2B and W2B5 contacts on ZnO

Rectifying contact formation on n-type bulk single crystal ZnO using novel W2B or W2B5 metallization schemes was studied using current-voltage, scanning electron microscopy and Auger electron spectroscopy (AES) measurements. When a single Au overlayer was used to reduce the metal sheet resistance, the contacts were ohmic for all annealing conditions due to outdiffusion of Zn through the metal. By sharp contrast, when a bilayer of Pt/Au was used on top of the boride layers, rectifying contacts with barrier heights of ∼0.4 eV for W2B were obtained. The highest barrier height of 0.66 eV was achieved for W2B5 annealed at 600 °C, although at this condition the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization.