Nonpolar AlGaN/GaN HFETs with a normally off operation

Abstract

Nonpolar AlGaN/GaN heterojunction field-effect transistors (HFETs) with a normally off operation have been demonstrated. The nonpolar (1–120) a-plane's epitaxial layers are grown on (1–102) r-plane sapphire substrates by metal organic chemical vapour deposition. We have found that a thicker AlN buffer layer achieves a GaN layer with a narrower full-width at half-maximum of the x-ray rocking curve and higher electron mobility. We have fabricated AlGaN/GaN HFETs with different gate directions. It is found that the drain current strongly depends on the gate directions, and higher drain current flows to the (0001) direction that is parallel to the hair-lined morphology. To realize a complete normally off operation, we have fabricated a-plane metal–insulator–semiconductor HFETs (MIS-HFETs) with a 2 nm-thick SiN as an insulator. The fabricated MIS-HFET exhibits a threshold voltage of +1.3 V with a high drain current of 112 mA mm−1. The presented MIS-HFETs will be desirable in next-generation power switching applications.