Gate Stack Design for Threshold Voltage Control of Gallium Nitride Power Transistors.

摘要

Gallium Nitride is an excellent material for power semiconductor applications due to its wide band gap, good thermal conductivity, high mobility and high breakdown field. The availability of high quality GaN on silicon substrates promotes GaN as a future low cost, high power semiconductor material. However, there are still challenges that need to be overcome before AlGaN/GaN devices can provide robust solutions for power applications.;Particularly challenging, is that high mobility GaN transistors are normally-on, which requires a negative gate bias to turn off devices. A gate stack design to enable enhancement mode operation of GaN transistor devices has been developed. Gate dielectrics to reduce losses due to leakage deposited by atomic layer deposition have been characterized and evaluated. SiO2 and HfAlO deposited by atomic layer deposition on GaN have been characterized electrically for the first time. The band alignment of these dielectrics with GaN as well as commonly used Al2O3 and HfO2 dielectrics has also been experimentally determined and reported for the first time. A novel device structure, termed the Flash MOS-HFET, has been designed, simulated and fabricated which allows for enhancement mode GaN transistor operation. This novel device has been characterized and materials and engineering concerns arising from the invented device have been addressed. An optimized Flash MOS-HFET device allows for continuous enhancement mode operation with high threshold voltage, high performance and low gate leakage facilitated by a gate insulator.