Temperature-Dependent Dynamic in GaN-Based MIS-HEMTs: Role of Surface Traps and Buffer Leakage

This paper reports an investigation of the trapping mechanisms responsible for the temperature-dependent dynamic-R_ON of GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs). More specifically, we perform the following. First, we propose a novel testing approach, based on combined OFF-state bias, backgating investigation, and positive substrate operation, to separately investigate the buffer-and the surface-related trapping processes. Then, we demonstrate that the dynamic R_ON of GaN-based MIS-HEMTs significantly increases when the devices are operated at high temperature levels. We explain this effect by demonstrating that it is due to the increased injection of electrons from the substrate to the buffer (under backgating conditions) and from the gate to the surface (under positive substrate operation). Finally, we demonstrate that by optimizing the buffer and by reducing the vertical leakage, substrate-related trapping effects can be completely suppressed. The results described within this paper provide general guidelines for the evaluation of the origin of dynamic R_ON in GaN power HEMTs and point out the important role of the buffer leakage in favouring the trapping processes.