Normally-off AlGaN/AlN/GaN/Si oxide-passivated HEMTs and MOS-HEMTs by using CF4 plasma and ozone water oxidization treatment

The letter reports normally-off device characteristics of Al0.26Ga0.74N/AlN/GaN oxide-passivated high electron mobility transistors (HEMTs) and metal-oxide-semiconductor HEMTs (MOS-HEMTs) grown on a Si substrate. Al2O3 was formed as the surface passivation oxide or gate dielectric on a thin AlGaN barrier layer by using a cost-effective ozone water oxidization technique. CF4 plasma was used to enable normally-off operation. For the gate dimensions of 1×100 µm2, the present oxide-passivated HEMT and MOS-HEMT (a control Schottky-gate HEMT) have demonstrated superior on/off-current ratio (Ion/Ioff) of 2.5×106 and 1×107 (3.9×103), maximum extrinsic transconductance (gm, max) of 154 and 175 (120) mS/mm, maximum drain-source current density (IDS, max) of 312 and 349 (300) mA/mm, two-terminal gate-drain breakdown voltage (BVGD) of −80 and −140 (−36) V, turn-on voltage (Von) of 1.2 and 1.3 (1) V, and three-terminal on-state breakdown voltage (BVDS) of 93 and 109 (48) V. Excellent BVGD and BVDS enhancements of 122% (288%) and 94% (127%) are achieved in the present oxide-passivated HEMT (MOS-HEMT) design.