Low Au Content Ohmic Contacts to N-Gaas Incorporating Sputtered Tungsten Oxide

Electron-beam (e-beam) evaporated low Au content NiGe(Au)W ohmic contacts with a contact resistance (Rc) as low as 0.15 Ω-mm have been reported. Due to the high melting point of W it is desirable to deposit this layer by means other than e-beam evaporation. However, the use of nearly oxygen-free sputtered W, yields contact resistances in excess of 0.7 Ω-mm. By replacing the sputtered W by a reactively sputtered metallic W oxide, containing ~25 at. % oxygen, the low contact resistance (Rc < 0.15 Ω-mm) is restored. Contacts employing a reactively sputtered W nitride in place of W oxide also yield high Rc’s (~0.75 Ω-mm). Auger depth profiles of the reacted contacts show a significant outdiffusion of Ga from the GaAs substrate in the presence the oxygenated W but not in the low oxygen and the W nitride contacts. These results and the fact that our previously reported e-beam evaporated W contacts also contain ~25 at. % oxygen, suggest an oxygen assisted ohmic contact formation mechanism.