False Surface Trap Signatures Induced by Buffer Traps in AlGaN/GaN HEMTs

Trap characterization methods, such as DLTS (Deep-Level Transient Spectroscopy), low-frequency transconductance (gm) dispersion, and pulse measurements are key techniques for reliability assessment in AlGaN-GaN HEMTs, where most of degradation effects are related to traps [1]. The aim of this work is to show that buffer traps can produce the same type of current-mode DLTS (I-DLTS) and pulsed-measurement signatures that are generally attributed to surface traps. This misleading behavior has been observed in AlGaN-GaN HEMTs of different technologies and confirmed/clarified by two-dimensional (2D) numerical device simulations. Enlightening this effect is important for reliability testing and the development of more reliable technologies, as it can completely hinder the correct identification of degradation mechanisms and the consequent, appropriate correction actions.