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 Al_0.26Ga_0.74N/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 (I_on/I_off) of 2.5×10⁶ and 1×10⁷ (3.9×10³), maximum extrinsic transconductance (g_{m, max}) of 154 and 175 (120) mS/mm, maximum drain-source current density (I_{DS, max}) of 312 and 349 (300) mA/mm, two-terminal gate-drain breakdown voltage (BV_GD) of −80 and −140 (−36) V, turn-on voltage (V_on) of 1.2 and 1.3 (1) V, and three-terminal on-state breakdown voltage (BV_DS) of 93 and 109 (48) V. Excellent BV_GD and BV_DS enhancements of 122% (288%) and 94% (127%) are achieved in the present oxide-passivated HEMT (MOS-HEMT) design.