Electroluminescence analysis of time-dependent reverse-bias degradation of HEMTs: a complete model

This paper analyzes the reverse-bias degradation of GaN-based HEMTs. Experimental evidence collected within this work demonstrate that, (i) when submitted to reverse-gate stress, HEMTs can show both recoverable and permanent degradation. (ii) recoverable degradation consists in the decrease in gate current and threshold voltage, which are ascribed to the simultaneous trapping of negative charge in the AlGaN layer, and of positive charge close to the AlGaN/GaN interface. (iii) permanent degradation consists in the generation of parasitic leakage paths. Results indicate that permanent degradation can occur even for stress voltage levels significantly lower than the “critical” voltage identified by step-stress experiments. Time-dependent analysis suggests that permanent degradation can be ascribed to a defect generation and percolation process. Results supports the existence of a “time to breakdown” (tBD) for HEMT degradation, which significantly depends on the stress voltage level.