W and WSix Ohmic contacts on p- and n-type GaN

W and WSi Ohmic contacts on both p- and n-type GaN have been annealed at temperatures from 300 to 1000 °C. There is minimal reaction (⩽100 Å broadening of the metal/GaN interface) even at 1000 °C. Specific contact resistances in the 10−5 Ω cm2 range are obtained for WSix on Si-implanted GaN with a peak doping concentration of ∼5×1020 cm−3, after annealing at 950 °C. On p-GaN, leaky Schottky diode behavior is observed for W, WSix and Ni/Au contacts at room temperature, but true Ohmic characteristics are obtained at 250–300 °C, where the specific contact resistances are, typically, in the 10−2 Ω cm2 range. The best contacts for W and WSix are obtained after 700 °C annealing for periods of 30–120 s. The formation of β-W2N interfacial phases appear to be important in determining the contact quality.