Electronic tunability and anisotropy in 2D P-N allotropes under strain

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 1.163 eV 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.