  We report the first observation of ferroelectric gating in AlScN barrier
wide-bandgap nitride transistors. These FerroHEMT devices realized by direct
epitaxial growth represent a new class of ferroelectric transistors in which
the semiconductor is itself polar, and the crystalline ferroelectric barrier is
lattice-matched to the substrate. The FerroHEMTs reported here use the thinnest
nitride high K and ferroelectric barriers to date to deliver the highest on
currents at 4 A/mm, and highest speed AlScN transistors with fmax larger than
150 GHz observed in any ferroelectric transistor. The FerroHEMTs exhibit
hysteretic Id Vgs loops with subthreshold slopes below the Boltzmann limit. A
control AlN barrier HEMT exhibits neither hysteretic, nor sub Boltzmann
behavior. While these results introduce the first epitaxial high K and
ferroelectric barrier technology to RF and mm wave electronics, they are also
of interest as a new material platform for combining memory and logic
functionalities in digital electronics.
