Silisyum karbür üzerinde galyum nitrat yüksek elektron hareketliliğine sahip transistörlerin (gan-on-sic hemt) güvenilirlik ölçümleri ve analizi

Gallium nitride (GaN) high electron mobility transistors (HEMTs) on semiinsulating SiC (GaN-on-SiC HEMT) have become the leading technology for high-power and high-frequency applications, yet their reliability is still under development. In particular, off-state operation under deep reverse bias is dominated by field-driven failure mechanisms such as impact ionization, hot-electron trapping, and gate and buffer leakage, which manifest as increased leakage currents, current collapse, and time-dependent breakdown. This thesis focuses on understanding and improving the off-state robustness of GaN-on-SiC HEMTs by systematically engineering the device layout, fabrication processes, and epitaxial design, using long-term off-state stress and leakage behavior as the primary evaluation criteria. After introducing GaN material properties, device structure, and relevant failure mechanisms, the thesis first establishes a baseline by characterizing the RFHTOL (RF-biased High Temperature Operating Life) behavior of the initial technology. Catastrophic failures under realistic RF stress motivated a series of geometric optimizations. By rearranging the lateral layout, in particular increasing the gate–drain spacing and rearranging the field-plate and drain pad connections, the breakdown voltage was significantly increased while maintaining essentially the same RF output power and efficiency. Next, fabrication-related reliability bottlenecks were addressed. Post-metal annealing and improved gate-foot etch resolved severe Q-point instability by restoring a true Schottky gate and eliminating residual SiN under the gate. An in-situ O2/Ar ion pre-gate treatment and a high-temperature PECVD first nitride layer were then introduced, reducing gate and drain leakage by more than an order of magnitude and virtually eliminating catastrophic HTRB failures up to 200 ◦C. These improvements were validated by DC-HTOL, HTRB, RF-HTOL, and step-HTRB tests. Finally, the thesis investigates three epitaxial engineering routes targeting electric field redistribution and buffer-related trapping. A detailed root-cause analysis of gate degradation under HTRB test, combining TEM, elemental analysis, and electrical data, show that an ultra-thin oxide layer beneath the gate enhance the impact ionization at the drain-side gate edge. A dedicated buffer-engineering as thinning the c-GaN and increasing carbon concentration via growth condition control redistributes the vertical field, and reduces the active impact-ionization volume. That results in a reduction of final gate and drain leakage after longterm HTRB. Building on this, two epitaxial concepts are also developed. An AlGaN/GaN/AlGaN back-barrier design achieves roughly 30% higher breakdown voltage and more than a two-fold increase in time-to-failure under HTRB, with preserved RF performance and strongly reduced dynamic dispersion. A novel Fe-free ultra-thin buffer architecture with only 200 nm total GaN thickness further improves breakdown voltage by approximately 78%, increases RF output power and transconductance, and yields an order-of-magnitude reduction in off-state leakage, with zero failures observed in HTRB over the investigated stress window. TCAD simulations and TEM analysis consistently show that these epitaxial concepts relax the peak electric field at the gate edge. Overall, the thesis demonstrates that off-state reliability of GaN-on-SiC HEMTs can be substantially improved without sacrificing RF performance by coordinated optimization of layout, process, and epitaxy, guided by field distribution and leakage-based reliability metrics.