Low-Loss and High-Voltage III-Nitride Transistors for Power Switching Applications

摘要

This paper describes recent technological advances on III-nitride-based transistors for power switching applications.Focuses are placed on the progress toward enhancing the breakdown voltage, lowering the ON -resistance, suppressing current collapse, and reducing the leakage current in AlGaN/GaNhigh-electron mobility transistors (HEMTs). Recent publications revealed that the tradeoff relation between ON -resistance andbreakdown voltage in AlGaN/GaN HEMTs exceeded the SiC limit and was getting close to the GaN limit; however, the breakdown voltage achieved was still lower than the theoreticalimpact ionization limit. A novel process featuring strain-controlled annealing with a metal stack, including Al gave rise to significant reduction in the sheet resistance in AlGaN/GaN heterostructures, suggesting the possibility of dramatic reduction in ON -resistance of GaN-based power devices. Some of the interesting approaches to suppress current collapse indicated that surface trapping effects must be controlled by theoptimization of surface processing as well as by the reduction of bulk traps in the epitaxial layers. Close correlation betweenthe local gate leakage current and point defects exposed on the free-standing GaN substrate demonstrated that further reductionof defects on bulk GaN substrates is truly required as future challenges.