Institute of High Pressure Physics

Researchers from our Institute used advanced ab initio simulations to unravel how atoms bond in key semiconductor materials like BN, AlN, GaN, InN, and graphene. The calculations confirmed that the valence band of GaN is divided into two separate subbands. The upper subband of GaN is composed of gallium sp and nitrogen p orbitals, while the lower subband consists of metal d and nitrogen s orbitals. Calculation of overlap integrals allowed to determine the bond order in tetrahedrally coordinated semiconductors. According to these results, bonding occurs between resonant p-states of nitrogen and sp³-hybridized metal orbitals in tetrahedral nitrides, allowing tetrahedral symmetry to be maintained. A similar resonant bonding mechanism is observed in hexagonal BN, where the p orbitals of nitrogen create three resonant states necessary for maintaining the planar symmetry of the lattice. BN bonding differs from that in graphene, where carbon states are fully sp²-hybridized. Additionally, π-type bonds in graphene have no ionic contributions, which leads to the formation of Dirac states with linear dispersion close to the K point, closing the band gap

Understanding these nuanced bonding mechanisms refines our fundamental picture of how these semiconductors and 2D materials behave and could directly impact the design of next-generation optoelectronic devices.

The publication is available in Open Access: Ab Initio Elucidation of the Nature of the Bonding of Tetrahedral Nitrides (BN, AlN, GaN, and InN), Hexagonal BN, and Graphene Paweł Strąk, Konrad Sakowski, Pawel Kempisty, Izabella Grzegory, Agata Kaminska, Stanislaw Krukowski. Materials 2025, 18, 2875.

Figure: The electronic properties of bulk wurtzite gallium nitride (GaN). The panels represent, from the leftmost: band diagram, projected density of states (PDOS) of the Ga (left) and N (right) atoms.