Degradation of AlGaN/GaN HEMTs below the “critical voltage”: a time-dependent analysis

This paper describes an extensive study of the reversebias degradation of AlGaN/GaN-based High Electron Mobility Transistors. The analysis was carried out by means of combined electrical characterization and timeresolved electroluminescence measurements. Results indicate that: (i) AlGaN/GaN HEMTs can degrade even below the “critical voltage” identified by means of stepstress experiments. (ii) during a constant voltage stress test, HEMTs can show both a recoverable and a permanent degradation. (iii) Recoverable degradation is ascribed to the accumulation of negative (positive) charge in the AlGaN layer (at the AlGaN/GaN interface). (iv) Permanent degradation is ascribed to a defect generation and percolation process.