Reliability and instabilities in GaN-based HEMTs

This talk reviews the physical mechanisms that limit the performance and the reliability of GaN-based high electron mobility transistors (HEMTs), by comparing experimental data with the results presented in the literature. We discuss the following relevant aspects: (i) exposure to high electric field, in the off-state, may induce a significant trapping of charge within the device; this may induce an increase in the on-resistance, or a shift in the threshold voltage, that may negatively affect the performance of the devices; (ii) trapping may also be induced by the presence of hot electrons which, accelerated by the electric field, may achieve enough energy to be injected into the buffer and/or in the barrier layer; (iii) several mechanisms can be responsible for the degradation of GaN-based HEMTs: the generation of gate leakage paths, the generation of defects due to hot electrons, the delamination of the passivation, electrochemical reactions at the surface; (iv) the breakdown voltage of HEMTs is often lower that the theoretical value, due to a number of mechanisms, including the existence of punch-through current components, vertical drain-bulk leakage, and impact ionization.