OFF-state drain reliability of enhanced mode AlGaN/GaN power HEMTs: TDDB and avalanche processes

The aim of this thesis work consists in the identification and modeling of the physical mechanisms that limit the stability and the performance of enhanced-mode AlGaN/GaN High Electron Mobility Transistors in OFF-state bias conditions. Initially, preliminary static characterizations have been carried out in order to evaluate DC performance and to determine which characteristics are of interest to evaluate the device degradation. Afterwards, constant voltage stress tests have been exploited to investigate the failure distribution by means of the shape factor of the Weibull plots and a degradation trend in temperature was observed. In order to address the physical reasons for the Weibull behavior, several experimental techniques (e.g. step stress, C-V, pulsed and electroluminescence measurements, sweep to breakdown) have been used. Eventually, a new device generation was evaluated in order to validate the formulated hypotheses.