Deep sub-60 mV/decade subthreshold swing in AlGaN/GaN FinMISHFETs with M-plane sidewall channel

AlGaN/GaN FinMISHFETs with m-plane sidewall surface channel and various fin widths (W_fin) were fabricated and characterized. The investigated devices have much higher current drivability due to the uniform and smooth surface of m-plane than those with the a-plane sidewall surface channel. The AlGaN/GaN FinMISHFETs with W_fin smaller than 36 nm exhibit normally-off operation, high Ion/Ioff ratio of 108, and remarkable subthreshold swing (SS) smaller than 40 mV/decade in the wide current range of at least three orders. Combined with a positive threshold voltage, SS values smaller than 60 mV/decade in a wide current rage of at least three orders are among the world's best subthreshold characteristics. Furthermore, when W_fin is 31 nm, the off-state drain current is as low as 10-12 A. We show that this sharp switch is due to the simultaneous turn-on of the 2-D electron gas and the m-plane sidewall surface channel. The simulation results are carried out to show the gate-induced variation of the electron concentration within the fin structure, and the assumption of considering gate width as a function of gate bias is also developed to explain the reason for deep sub-60mV/decade in the demonstrated devices.