Alloy-driven modulation of electronic, mechanical and optical properties in 2D BPN-Ga1-xAlxN monolayers

In the present work, we report the effects of alloying on the structural, electronic, mechanical, and optical properties of biphenylene (BPN)-Ga${}_{\text{1-x}}$Al${}_{\text{x}}$N monolayers based on the density functional theory calculations. We found that the considered monolayers exhibit significant structural stability, as evidenced by their high cohesive energy and low lattice parameters, indicating a tight lattice and robust bonding network. Phonon dispersion analysis further confirms the dynamical stability of these monolayers, since no imaginary phonon modes were observed along the 2D Brillouin zone (BZ). The electronic band structure calculations indicate that all the systems under consideration are nonmagnetic direct gap semiconductors with a band gap located at $\Gamma$-point in BZ. Both standard PBE and hybrid HSE06 functionals were employed in the calculations to accurately investigate the electronic properties of the systems. The band gap increases from 2.81 eV to 3.64 eV with higher Al content, shifting optical absorption from the visible to UV region, which makes it suitable for optoelectronic devices such as UV photodetectors and LEDs. The mechanical properties, including Young’s modulus and Poisson’s ratio, demonstrate increased stiffness and reduced compressibility with higher Al concentrations. Additionally, the optical properties exhibit a blue shift in absorption peaks with increasing Al content as revealed by the dielectric function calculations. This work contributes to the understanding of 2D materials in next-generation semiconductor and optoelectronic technologies, highlighting the potential and tunability of BPN-Ga${}_{\text{1-x}}$Al${}_{\text{x}}$N monolayers for advanced applications.