Characterization and reliability of vertical n-type gallium nitride Schottky contacts

Abstract

Silicon- and silicon carbide-based power devices have dominated the power electronics industry. For many emerging high-current and high-power applications, vertical transport gallium nitride (GaN)-based devices are more desirable. In this study, a series of reduced-defect, vertical n-type GaN Schottky contacts were fabricated and subjected to high-current density accelerated lifetime tests to understand the physics of contact degradation and compare the reliability of different metallization types and process cleans. Tested Schottky metals included molybdenum, molybdenum-gold, and chromium-gold. Process cleans compared were a piranha etch and a hydrofluoric acid etch. Pre-stress electrical characterization confirmed functioning Schottky contacts and determined device electrical performance parameters. Using a stress-measure- stress system, we obtained results of high-current density accelerated lifetime testing of 170 hours at current densities of 2.3 kAcm-² that showed both catastrophic and non-catastrophic failures across all metallization types and process cleans. While comparative analysis showed that molybdenum was the most reliable, identified experimental testing and non-ideal fabrication issues limited the conclusivity of the results. The identified constraints and initial comparative results serve to inform future Schottky contact structural design and fabrication for future optimized testing