Role of buffer doping and pre-existing trap states in the current collapse and degradation of AlGaN/GaN HEMTs

The aim of this work is to quantitatively investigate the influence of buffer doping on the current collapse of AlGaN/GaN HEMTs, and to analyze the contribution of trap states to the increase in current collapse detected after reverse-bias stress. The study was carried out on GaN-based HEMTs with increasing levels of iron doping in the buffer, which were submitted to drain current transient measurements and reversebias stress. Results demonstrate that the use of Fe-doping may significantly impact on current collapse; moreover, we demonstrate that the increase in current collapse detected after reverse-bias stress is not due to the generation of new types of defect, but to the increase in the signal of the defects which were already present before stress.