Thermally stable, low-resistance NiInWN_x ohmic contacts to n-type GaAs prepared by sputter deposition

A new thermally stable, low-resistance In-based ohmic contact to n-type GaAs has been developed. The contacts consist of ion-beam sputtered Ni (5 nm)/In (5 nm)/Ni (5 nm) layers with a magnetron sputtered WNx overlayer. A low-contact resistance of ∼0.3 Ω mm was obtained by rapid thermal annealing at 750°C for ∼5 s. The contact resistance and the excellent contact morphology remained unchanged after annealing at 400°C for more than 100 h. The present deposition technique provides several advantages over previously reported electron-beam evaporated In-based contacts. In particular, the ability to deposit a thick WNx overlayer simplifies GaAs integrated circuit (IC) fabrication by (a) eliminating the need for separate diffusion barrier deposition and patterning steps, and (b) providing for low-sheet resistance (∼2 Ω/D'Alembertian) IC interconnect capabilities. In addition, sputter deposition allows for the controlled incorporation of n-type dopants into the metallization if further reduction of the contact resistance is required.