Fabrication of normally-off AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors by photo-electrochemical gate recess etching in ionic liquid

We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of similar to 2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from -10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582V. (C) 2016 The Japan Society of Applied Physics