Normally-OFF AlGaN/GaN MOS-HEMT with a two-step gate recess

This paper presents results of normally-off AlGaN/GaN MOS-HEMTs fabricated with a two-step gate recess technique which includes a chloride based Inductively Coupled Plasma (ICP) etch followed by HCI and NH₄OH surface treatment. The latter can effectively smoothen evenly the ICP etched surface. The two-step gate recessed device with atomic layer deposited (ALD) Al₂O₃ as gate dielectric delivers a threshold voltage (V_th) of +1V and a maximum current density per gate width (I_max) of up to 0.583 A/mm which is 90% that of an un-recessed gate depletion-mode AlGaN/GaN HEMT device (V_th of -3.5V) fabricated from the same epitaxial wafer.