Reliability studies of AuGe/Ni/Au ohmic contacts to MESFETs by accelerated thermal aging tests

Optimally alloyed AuGe/Ni/Au source-drain ohmic contacts to MESFETs with very low contact resistance (R_c) of the order 0.05 - 0.07 Omega-mm were obtained after rapid thermal alloying at 400degC. We have studied the degradation of ohmic contacts at elevated temperatures for 4000 hours. Ohmic contact test structures were subjected to accelerated life test temperatures at 185degC, 200degC and 230degC. We found that the drifts in R_c of the optimally alloyed contacts after thermal aging were as low as +13%, which are possibly one of the lowest drifts reported hitherto. This low drift may be due to the formation of thermally stable compounds and their nature at the ohmic contact interfaces, and the access regions during optimum alloying.