Electronic and Optical Properties of Novel Janus Monolayer X2AsP (X = B, Al, Ga)

Two-dimensional (2D) materials offer an optimal basis to realize intriguing quantum phenomenon and develop versatile nanoscale devices. The recent successful synthesis of 2D double-layer honeycomb (DLHC) AlSb revealed that it possesses interesting semiconducting properties, which inspires further investigation into robust DLHC materials. In this theoretical study, we theoretically predict novel Janus DLHC materials X2AsP (X = B, Al, Ga), from which Al2AsP and Ga2AsP are found to possess dynamic and mechanical stability, confirmed through first-principles calculations. Among the two stable materials, Al2AsP has an indirect bandgap of 1.964 eV, whereas Ga2AsP has a direct bandgap of 0.378 eV. Both of these monolayers are found to have low values of carrier effective masses, implying their potential for application in high-speed nanoelectronic devices. In addition to the electronic properties, the optical properties of X2AsP are calculated. Al2AsP possesses a high absorption co-efficient of 14.1×10⁵ cm^-1 and a narrow linewidth of 1.68 eV for out-of-plane polarization of incident light, indicating that the material may find application as a selective UV detector. Besides, for in-plane polarization, a moderate linewidth (3.55 eV) and a high value of peak reflectance of 48.45% are obtained for Ga2AsP, implying its potential usage in mid-UV and far-UV region. Our findings, such as, direct bandgap, low effective mass and desirable optical properties highlight the potential application of novel Janus 2D monolayer, X2AsP in high-performance, and efficient electronic and optoelectronic devices.