Degradation mechanisms of Ti/Al/Ni/Au-based Ohmic contacts on AlGaN/GaN HEMTs

The degradation mechanism of Ti/Al/Ni/Au-based Ohmic metallization on AlGaN/GaN high electron mobility transistors upon exposure to buffer oxide etchant (BOE) was investigated. The major effect of BOE on the Ohmic metal was an increase of sheet resistance from 2.89 to 3.69 Ω/◻ after 3 min BOE treatment. The alloyed Ohmic metallization consisted 3–5 μm Ni-Al alloy islands surrounded by Au-Al alloy-rings. The morphology of both the islands and ring areas became flatter after BOE etching. Energy dispersive x-ray analysis and Auger electron microscopy were used to analyze the compositions and metal distributions in the metal alloys prior to and after BOE exposure.