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 Al2O3 serving as both gate dielectric under the gate electrode and passivation layer in the access region was used. It was found that the Al2O3 was superior to SiNx in increasing the 2-D electron gas (2DEG) density and thereby reducing the access resistance. In addition, the OFF-state leakage current (I-off) in these AlN/GaN MOSHFETs was reduced by four orders of magnitude to 7.6 x 10(-5) mA/mm as a result of the Al2O3 gate 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 low I-off. The MOSHFETs with 1-mu m 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.