Recessed-gate GaN-based MIS-HEMTs Performance Dependence on Recess Depth

We studied the electrical performance of recessed-gate GaN-based MIS-HEMTs, particularly the non-monotonic dependence of transconductance gm on recess depth of the AlGaN barrier in the channel region. From planar structure with original AlGaN barrier thickness in the channel (dCH) of 25 nm, reducing dCH to 15 nm by dry-etching, threshold voltage (VTH) shift positively while the maximum transconductance gm,max increased. However, when the dCH was further reduced to 6 nm, while VTH still shifted towards positive voltage direction, gm.max was significantly decreased. Our results suggest that for a given MIS-HEMT structure, there is an optimum recess depth that will result in the highest gm.max. Our findings could provide important guidelines for achieving optimal performance from normally-off recessed-gate GaN-based MIS-HEMTs designed using interface charge engineering.