Gallium Oxide and Gallium Nitride-based devices for high-power applications: characterization, reliability, and modelling

This thesis reports on the experimental analysis and modeling of the physics and reliability of GaN and β-Ga2O3 power devices. The work was carried out in collaboration with several partners, that provided state-of-the-art samples to be investigated, especially in terms of the electrical performances, stability, and long term reliability. The first part of the experimental section is dedicated to the analysis of β-Ga2O3 devices. We first analyzed the stability, conduction properties, and deep levels of nitrogen-implanted β-Ga2O3 Schottky Barrier Diodes; next, we discuss about the physics of the gate module of β-Ga2O3 MOSFETs, in terms of charge trapping and leakage current. Then, we analyzed vertical GaN devices. Starting from the analysis of test structures (Schottky diodes and MOS capacitors) required to optimize the fabrication processes, we then moved to the analysis of the stability of vertical transistors, thus enabling to develop physical models to explain trapping effects and degradation. After that, the robustness of p-GaN gate HEMTs was considered. Thanks to an advanced analysis based on DC measurements, electroluminescence spectrum and threshold voltage transients, we proposed a novel degradation model that suggests a fundamental contribution of the injected holes at high temperature/high bias. Finally, the last chapter briefly revise the main results in the field of the device processing obtained during the exchange semester at the Nagoya University.