Investigation of Electromigration Degradation Mechanism in Ti/Pt/Au Ohmic Contacts to p-GaAs Under High Current Density Stress

The degradation mechanism of Ti/Pt/Au ohmic contacts to p-GaAs was identified experimentally under high direct-current density stress in detail. A revised measuring structure was designed based on the circular transfer length method (CTLM), in which the high current density of $0.8\times 10^{5}$ A/cm 2 was applied vertically, while the contact resistance was measured horizontally between two contact electrodes. According to revised CTLM, the specific contact resistance was measured during stress. The results indicated that specific contact resistance showed an exponential dependence on the aging time. The depth profiling results obtained from the Auger electron spectroscopy showed that Pt penetrated into the Au layer during stress. Furthermore, some voids were observed at the Au/Pt interface, and intermixing began to form within metal layer during stress. These results demonstrated that the degradation of Ti/Pt/Au ohmic contacts to p-GaAs was attributed mainly to the electromigration and Joule heating along the current direction under high current density.