Reliability in GaN-based devices for power applications

This paper analyzes two important reliability issues in AlGaN/GaN devices: positive bias temperature instability (PBTI) and time-dependent dielectric breakdown (TDDB). The summarized results of our previous PBTI studies in MOS-HEMTs show that the threshold voltage degradation in devices with SiO ₂ as gate dielectric is characterized by a universal decreasing behavior of the trapping rate parameter and is ascribed to charge trapping in the SiO ₂ and at the SiO ₂ /GaN interface. On the contrary, the degradation observed in Al ₂ O ₃ -and AlN/Al ₂ O ₃ -gate stacks is mainly attributed to charge capture in the pre-existing dielectric traps with a negligible interface state generation. Additionally, the insertion of a thin AlN layer impacts on the device reliability because larger trap density, faster charge trapping, wider trap energy distribution and slower charge release are observed compared with devices without this layer. The dielectric importance of GaN-based devices has been also investigated in Schottky Barrier Diodes (SBDs) with a gated edge termination (GET). Our recent TDDB results indicate a narrower Weibull distribution, and a longer time to failure in devices with a double GET layer structure and with a thick passivation layer (2 GET-THICK) than in single GET devices with a thin passivation (1 GET-THIN). Therefore, the former structure is more suitable for high-power and high-Temperature applications.