Quasi-2D Ca2X (X = C, Si, Ge, Sn, Pb) hexagonal intermetallic monolayer compounds: Comprehensive and comparative study on the electronic properties and strong anisotropic photo-response

• The 2D Ca 2 X (X = C, Si, Ge, Sn, Pb) monolayer compounds were explored for their optoelectronic applications using computational tools. • These materials are indirect bandgap materials, except for Ca 2 C, which exhibits metallic feature. • These materials exhibit strong anisotropic behaviour in response to the polarization directions of the light field. • Their polarization-dependent reflection coefficient indicates that they are useful for antireflective coating materials. Quasi-two-dimensional (2D) materials have garnered significant research interest due to their fascinating physical properties and diverse potential applications across various fields. Here, we investigate the electronic properties and anisotropic photo-response of quasi-2D monolayer hexagonal intermetallic compounds based on ultrathin Ca 2 X (X = group IVA elements) films using computational tools. Electronic investigations indicate that these monolayer compounds are indirect-band-gap semiconductors, except for the Ca 2 C monolayer, which exhibits metallic features. The calculated density of states (both total and projected) for these compounds corroborates the corresponding electronic band structures. The included spin–orbit coupling (SOC) for heavy elements like Sn and Pb exhibits the band splitting in the valence band of Ca 2 Sn and Ca 2 Pb monolayers. The obtained cohesive energy reveals that the Ca 2 C is the most stable structure. However, the structural stability is slightly reduced when the X-atom is moved from top to bottom within group IVA. The investigated materials exhibit strong anisotropic dielectric behavior in response to the polarization directions of the light field (in-plane and out-of-plane). These materials exhibit strong light absorption across the infrared (IR) to visible to low-energy ultraviolet (UV) spectrum. A more intense light absorption is also noticed in the X-ray region. Hence, these are excellent for absorption band-pass and stop filters. The calculated refractive index is the highest for the Ca 2 C monolayer and exhibits an anisotropic dispersion along the x- and z-directions. Moreover, these materials can also be realized as polarization-dependent reflection and transmission band filters, which are useful for antireflective coating materials. The investigated properties indicate that these materials have great potential in numerous optoelectronic device applications.