  Ultra-wide bandgap (UWBG) semiconductors are poised to transform power
electronics by surpassing the capabilities of established wide bandgap
materials, such as GaN and SiC, owing to their capability to operate at higher
voltage, frequency, and temperature ranges. While bulk group-III nitrides and
their alloys have been extensively studied in the UWBG realm, their
two-dimensional counterparts remain unexplored. Here, we examine the stability
and electronic properties of monolayers of ordered boron-based group-III
nitride alloys with general formula BxM1-xN, where M = Al, Ga. On the basis of
ab initio calculations we identify a number of energetically and dynamically
stable structures. Instrumental to their stability is a previously overlooked
out-of-plane displacement (puckering) of atoms, which induces a polar ordering
and antiferroelectric ground state. Our findings reveal the energy barrier
between metastable ferroelectric states is lowered by successive switching of
out-of-plane displacements through an antiferroelectric state.
