Stability of Ti/Al/ZrB2/Ti/Au ohmic contacts on n-GaN

Abstract

Ohmic contacts on n-GaN using a novel Ti/Al/ZrB2/Ti/Au metallization scheme were studied using contact resistance, scanning electron microscopy and Auger electron spectroscopy (AES) measurements. A minimum specific contact resistivity of 3×10−6Ωcm2 was achieved at an annealing temperature of 700°C. The lowest contact resistance was obtained for 60s anneals. The contact resistance was essentially independent of measurement temperature, indicating that field emission plays a dominant role in the current transport. The Ti and Al in the contact stack began to outdiffuse to the surface at temperatures of ∼500°C, while at 1000°C the B also began to migrate to the surface. By this latter temperature, AES showed almost complete intermixing of the metallization even though the contact morphology was still smooth. The boride appears susceptible to getting of residual water vapor during sputter deposition.