  Novel devices such as tunneling field-effect transistors (FETs) and
ferroelectric FETs have been demonstrated to break the subthreshold swing (SS)
limit with sub-60 mV/decade switching for further low voltage/low power
applications. In this paper, SS of sub-60 mV/dec was firstly observed in
InAlN/GaN high electron mobility transistors (HMETs): an average SS of 30
mV/dec over three orders of magnitude in drain-source (Ids) and a minimum
point-by-point SS of 15 mV/dec were achieved in the InAlN/GaN HEMTs with gate
length (Lg) of 40 nm. It is found that SS decreases with drain-source voltage
(Vds) as well as Lg, and falls below 60 mV/dec when Lg < 100 nm. The decrease
of SS as the device dimension scales down is attributed to the tunneling of
high energy electrons from channel to the surface. The SS decreasing with the
nanoscale gate length shows the great potential of the InAlN/GaN HEMTs to be
applied in future logic switches.
