Low-Leakage-Current AlN/GaN MOSHFETs Using Al₂O₃ for Increased 2DEG

Metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) were fabricated with an AlN/GaN heterostructure grown on Si substrates. A 7-nm Al2O3serving as both gate dielectric under the gate electrode and passivation layer in the access region was used. It was found that the Al2O3was superior to SiNxin increasing the 2-D electron gas (2DEG) density and thereby reducing the access resistance. In addition, the off-state leakage current (Ioff) in these AlN/GaN MOSHFETs was reduced by four orders of magnitude to 7.6 × 10-5mA/mm as a result of the Al2O3gate dielectric, compared to that of AlN/GaN HFETs. Meanwhile, the subthreshold slope was improved to a nearly ideal value of 62 mV/dec because of the extremely lowIoff. The MOSHFETs with 1-μm gate length exhibited good DC characteristics. A maximum drain current of 745 mA/mm and a peak extrinsic transconductance of 280 mS/mm were achieved.