Optoelectronic and Piezoelectric Properties of Novel Janus Monolayer Al ₂ AsX ( <i>X</i> = Sb, P)

In this theoretical study, we introduce novel Janus double‐layer honeycomb (DLHC) materials, Al 2 AsX ( X = Sb, P). The dynamic stability of these materials is demonstrated through positive phonon dispersion and mechanical stability via Born's criterion. The two monolayers investigated exhibit distinct electronic properties; Al 2 AsSb presents a direct bandgap 0.435 eV, whereas Al 2 AsP features an indirect bandgap of 1.964 eV. Notably, under biaxial strains ranging from −6% to 8%, tunability of the bandgap is observed for both monolayers. An indirect‐to‐direct bandgap transition in Al 2 AsP at +3% strain enhances its suitability for optoelectronic applications by improving quantum efficiency. Furthermore, the study highlights the optical properties of the DLHC monolayers under strain, where the Al 2 SbAs monolayer demonstrates a high absorption coefficient (14.78 × 10 5 cm −1 ) coupled with a narrow full width at half maximum (FWHM) indicating its potential as a selective ultraviolet absorber. The birefringent characteristics of Al 2 AsX ( X = Sb, P) may also find applications in optical waveplates and polarization‐controlled spontaneous emissions. Additionally, due to the absence of inversion symmetry, the piezoelectric properties of Al2SbAs ( d 11 = 2.7022 pm/V) are revealed, outperforming other known 2D piezoelectric materials such as WS 2 and α‐quartz. Our findings underscore the considerable potential of monolayer Al 2 AsX ( X = P, Sb) for the advancement of innovative optoelectronic and piezoelectric devices.