Sub-60 mV/decade Switching via Hot Electron Transfer in Nanoscale GaN HEMTs

In this letter, a subthreshold swing (SS) of sub-60 mV/dec is for the first time observed in InAlN/GaN high electron mobility transistors (HMETs). With a 40-nm gate length ( ${L} _{{\text {g}}}$ ), an average SS of 30 mV/dec over three orders of magnitude in drain current ( I d) and a minimum point-by-point SS of 15 mV/dec are achieved. The transistor body factor ( m ) of 4.99/6.98 (in forward/reverse sweep) determined from temperature-variation measurements indicates that the sub-60 mV/dec SS characteristic is not attributed to the negative capacitance effect. The negative differential resistance (NDR) of gate current ( I g) is observed and the hot electron transfer from channel to gate is believed to account for the sub-60 mV/dec SS characteristic. It is further confirmed by the fact that, SS decreases as drain-source voltage ( V ds) increases and L g decreases. Due to the increased V ds and decreased $L_{\text {g,}}$ the channel lateral electric field is strengthened, leading to the hot electron formation and thus the enhanced effect of hot electron transfer on the SS. This sub-60 mV/dec SS characteristic in the nanoscale devices shows the great potential of the InAlN/GaN HEMTs to be applied in future logic switches.