(Invited) Microstrucutural Characterizaton of Stressed AlGaN/GaN HEMT Devices

Abstract

Defects produced from the application of electrical stress to AlGaN/GaN high electron mobility transistors were studied. The defects observed include micron-length cracking of the AlGaN and GaN layers, a reaction of the native oxide interfacial layer between the gate contact and AlGaN epilayer resulting in a band defect, and an electrochemical pitting reaction between the gate contact and AlGaN epilayer. These defects were characterized using a combination of surface etching chemical deprocessing, top-down scanning electron microscopy, and cross sectional transmission electron microscopy. The cracks in the AlGaN and GaN layers are shown to lengthen under application of electrical stress. The band defects appear to coincide with a large increase in gate leakage current associated with the critical voltage during electrical stressing. However, continued electrical stressing past the critical voltage results in pitting of the AlGaN epilayer under and near the gate contact. Simulations of the electric field lines from these pitted devices match the defect morphology across a range of different stress conditions and device structures and geometries.