Reliability of GaN-based HEMTs: electrical, optical and physical investigations

The identification of failure modes and mechanisms which may affect the reliability of GaN-based High Electron Mobility Transistors is extremely important for the application of this technology to microwave and millimeterwave systems, and for the development of high-efficiency GaN power electronics. GaN HEMT reliability has been the subject of a large number of studies which identify specific failure modes, not previously observed in Si and GaAs devices. If one looks at the data available in the literature, the situation seems paradoxical: at room temperature, in off-state conditions, or when the gate-drain Schottky junction is reverse biased by a sufficiently high voltage VGD, the prevailing failure mode is a catastrophic increase of gate leakage, which takes place within minutes. This failure mode is accompanied by an increase in trap density (presumably within the AlGaN barrier) and dispersion effects, and closely resembles time dependent dielectric breakdown effects of MOS structures, with a very low thermal activation energy