Advanced TCAD modeling of charge trapping phenomena in ALGAN/GAN and ALSCN/GAN HEMTs

Gallium nitride (GaN) High Electron Mobility Transistors (HEMTs) enable high-efficiency power conversion and RF applications due to their wide bandgap, high critical field, and strong polarization-induced 2DEG. However, process-induced defects in epitaxy, interface engineering, and passivation introduce bulk and surface traps, limiting reliability and industrial adoption. This thesis develops an advanced TCAD-based framework to analyze gate leakage in enhancement-mode p-GaN HEMTs and charge trapping dynamics in depletion-mode AlGaN/GaN and AlScN/GaN HEMTs. The work bridges experiments and simulations, establishing quantitatively calibrated models linking material defects to device degradation. For p-GaN gate HEMTs, a comprehensive gate-leakage model combining field-assisted and trap-assisted tunneling reproduces experimental $I_\mathrm{G}$–$V_\mathrm{G}$ and $I_\mathrm{D}$–$V_\mathrm{G}$ characteristics, highlighting the influence of corner fields at the metal/p-GaN interface. In AlGaN/GaN HEMTs, combined DC, pulsed I–V, and HTRB step-stress analysis identifies deep Fe-related acceptor traps in the buffer and donor-like traps at the SiN/GaN-cap interface as the main degradation drivers. Pulsed measurements reveal incomplete detrapping of Fe centers causing current collapse, while donor traps stabilize surface potential. HTRB stress induces drain current drift via field-assisted detrapping at the passivation interface. Extending the study to AlScN/GaN HEMTs, enhanced spontaneous polarization increases 2DEG density and transconductance. Experimental and simulation analyses reveal three degradation pathways: under-gate acceptor buildup causing $V_\mathrm{th}$ shifts, donor detrapping reducing transconductance, and field-assisted gate leakage affecting drain current. This highlights the performance–reliability trade-off and emphasizes interface quality and barrier thickness optimization. Overall, the thesis establishes a coherent physical framework linking microscopic defects to macroscopic degradation across p-GaN, AlGaN/GaN, and AlScN/GaN HEMTs. The methodology enhances predictive TCAD modeling for GaN device reliability and provides guidelines for interface and barrier engineering, laying the groundwork for future electro-thermal and RF stress studies.