Low-Leakage-Current AlN/GaN MOSHFETs Using $\hbox {Al}_{2}\hbox {O}_{3}$ 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 SiN_x 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 × 10^-5 mA/mm as a result of the Al₂ O₃ 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-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.