Failure Process of GaN-HEMTs by Repetitive Overvoltage Stress

Failure process by overvoltage stress in GaN-HEMTs is discussed by burst UIS waveforms and C-V characteristics shift. One of the critical disadvantages of GaN-HEMTs is its lack of the UIS withstanding capability, because there is no removal structure of holes, which generated by the avalanche breakdown. Although overvoltage margin for the GaN power converters has been discussed by dynamic breakdown voltage, failure process by overvoltage stress has not been discussed sufficiently. This paper shows that overvoltage stress generated local shunt path between drain and substrate, graduated dielectric breakdown and hole trap/de-trap were observed by repetitive overvoltage stress. These results verify catastrophic failure of GaN-HEMTs by overvoltage stress is ascribed to a percolation process activated by the high-vertical electric field in hetero-epitaxial layers.