Thermal stability of ohmic contacts to n-GaAs formed by scanned electron beam processing

Abstract

Alloyed Au–Ge/Ni and sintered Au/Pd/Ge and Au/Pd/Ni/Ge ohmic contacts were formed on n-GaAs using scanned electron beam processing. Thermal aging studies at elevated temperatures in the range 150–500 °C reveal that sintered ohmic contacts have a much higher resistance to thermal degradation than conventionally alloyed Au–Ge/Ni contacts. Activation energy plots of failure time as a function of aging temperature indicate that sintered Au/Pd/Ni/Ge ohmic contacts have much longer operating life (∼106 h for an eightfold increase in ρc at 300 K) than both alloyed Au–Ge/Ni and sintered Au/Pd/Ge ohmic contacts. Studies on the effects of polyimide and rf sputtered SiO2 passivation layers on the stability of ohmic contacts reveal that polyimide surface passivated contacts exhibit better stability than those passivated with SiO2 . From Arrhenius activation energy analysis, there is strong evidence to suggest that a single degradation mechanism is responsible for ohmic contact failure over the full range of aging temperatures from 150 to 500 °C.