Controlling the Electro-Optical Properties of an AlSb Monolayer with a DLHC Structure through Phosphorus Alloying: A DFT Study

The experimental knowledge of the AlSb monolayer with a double-layer honeycomb structure is largely based on a recent publication [Le Qin et al., ACS Nano 2021, 15, 8184]. In the present work, we aim to explore the effect of phosphorus alloying on the structural, electronic, and optical properties of the AlSb monolayer (AlSb_xP_1-x). Phonon dispersion curves and cohesive energies, along with the Born criterion, demonstrate the stability of these structures. Our results show that with increasing P-concentration (from 0.375 to 1.0), the bandgaps increase to 1.25 eV, PBE (1.15 eV, PBE + SOC) for the alloyed AlSb structure with 0.875 P content, and an increase of 0.95 eV (PBE) and 0.56 eV (PBE + SOC) compared to that of the pristine AlSb bandgap. The largest bandgap is calculated to be 1.7 eV, PBE (1.65, PBE + SOC) for the AlP monolayer. Interestingly, for all P-concentrations, the bandgaps are direct, signifying potential applications of the material in photovoltaic applications. For P-contents from P = 0 to 0.375, the bandgap initially slightly decreases. The adsorption spectra are also found to depend on the concentration of P-dopant, where low concentration is found to be better than the high concentration for adsorption in the visible light range, while high concentration is better than low concentration for ultraviolet radiation. The variation of the bandgap with P-dopant concentration suggests the potential of these monolayer alloys for tunable bandgap engineering and application in future nano-optoelectronic devices.