Fabrication of Normally Off AlGaN/GaN MOSFET Using a Self-Terminating Gate Recess Etching Technique

A self-terminating gate recess etching technique is first proposed to fabricate normally off AlGaN/GaN MOSFET. The gate recess process includes a thermal oxidation of the AlGaN barrier layer for 40 min at 615°C followed by 45-min etching in potassium hydroxide solution at 70°C, which is found to be self-terminated at the AlGaN/GaN interface with negligible effect on the underlying GaN layer, manifesting itself easy to control, highly repeatable, and promising for industrialization. The fabricated device based on this technique with atomic layer deposition Al₂O₃ as gate insulator exhibits a threshold voltage as high as 3.2 V with a maximum drain current over 200 mA/mm and a 60% increased breakdown voltage than that of the conventional high electron mobility transistors.