Electronic Tunability and Anisotropy in 2D PN Allotropes under Strain

Abstract

Two-dimensional phosphorus–nitrogen (P--N) allotropes are emerging as promising candidates for advanced nanoelectronic and optoelectronic applications. Using density functional theory, we investigated four monolayers: phosphorene (P4) and three P–N derivatives (P2N2, P3N, and PN3). Cohesive energy calculations show that P2N2 and PN3 are more stable than P4, with phonon spectra confirming their dynamical stability. Electronic analysis reveals diverse bandgap behaviors: a tunable direct bandgap in P4, stable indirect bandgaps in P2N2 and P3N, and the smallest bandgap among the studied structures in PN3. Strain engineering, applied through biaxial and uniaxial deformations from -5% to +5%, further highlights distinctive responses, including indirect-to-direct bandgap transitions in P4, strong anisotropy in PN3 (bandgap up to 1.163eV along the a-axis), and moderate variations in P2N2. These results indicate that P--N two-dimenaional allotropes combine thermodynamic stability with tunable and anisotropic electronic properties, positioning them as versatile platforms for strain-engineered devices.