Deep sub-60 mV/dec subthreshold swing independent of gate bias sweep direction in an in situ SiN/Al_0.6Ga_0.4N/GaN-on-Si metal-insulator high electron mobility transistor

In this Letter, we demonstrated deep sub-60 mV/dec subthreshold swings (SS) independent of gate bias sweep direction in GaN-based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) with an Al0.6Ga0.4N/GaN heterostructure and in situ SiN as gate dielectric and surface passivation. Average SS values of 22 and 29 mV/dec over 3-4 orders of drain current (I-D) swing were measured during forward and reverse sweeps, respectively, in a 75-nm gate length (L-G) device. Sub-60 mV/dec SS was also observed in the GaN MISHEMTs with longer L-G up to 350 nm. The intrinsic physical mechanisms of deep sub-60 mV/dec SS were comprehensively studied. The observed negative differential resistance in the gate current, the kinks in the output I-D-V-D curve, and the capacitance spike in the depletion region of the C-V curves suggest that the capture and emission of electrons in the traps are the dominant physical mechanisms responsible for the small SS.