Computational Exploration of Stable 2D Ultra-Wide Bandgap Hexagonal Group III-Nitride Alloys*

Wide bandgap semiconductors like GaN and SiC enhance radio frequency (RF) amplifiers, power electronics, and military technologies by offering fast switching and low resistance. Additionally, two-dimensional materials hold promise for improving transport characteristics and field control in RF and power devices. In this study, we investigate monolayer two-dimensional hexagonal Group III-nitride alloys (Al_xB_1-xN, Ga_xB_1-xN, In_xB_1-xN), whose stable compositions and crystal structures have not been fully explored. Using first-principles calculations, we demonstrate that pure hexagonal monolayers of AlN, GaN, and BN are stable due to their strong covalent bonding and hexagonal lattice structures, while alloy compositions with x=0.50 and 0.75 exhibit pronounced phonon instabilities within planar lattices. Our detailed investigation into puckering has led us to find unique, energetically and dynamically stable puckered lattices characterized by significant distortions of nitrogen atoms from the planar h-BN structure. Some of these puckered structures are particularly intriguing as they break the inversion symmetry and have potential to exhibit out-of-plane polarization along the c-direction. These computational insights into manipulating 2D group-III nitrides through alloying will provide guidance for experimental synthesis and potential exploration of these alloys in next-generation electronic, optoelectronic, and thermoelectric devices.