Two-dimensional materials have been recognized as highly promising in next-generation optoelectronic devices and thermal management applications. In this study, we explore two distinct structural phases, $2H$ and $1T$, to elucidate the impact of structural modifications on the electro-optical and thermal transport properties of ${\mathrm{ZrSi}}_2{\mathrm{N}}_4$ monolayer. Our results reveal remarkable differences in the electronic band structure and density of states between the trigonal prismatic ($2H$-phase) and octahedral ($1T$-phase) coordination of Zr atoms. The band gap decreases from 2.736 eV ($2H$ phase) to 2.233 eV ($1T$ phase), accompanied by momentum shift in the valence band maximum at high-symmetry points in the Brillouin zone. Also, the effective masses of electrons and holes are substantially lowered in specific directions for the $1T$ phase indicating improved carrier mobility. Besides, Young's modulus increases while the dielectric constant decreases due to octahedral coordination of Zr atoms in the $1T$ phase. Moreover, the optical absorption spectra are significantly tuned due to distinct charge localization in the respective structural phases. Intriguingly, a notable enhancement in lattice thermal conductivity is observed for the $1T$ phase at room temperature owing to increased phonon lifetimes (reduced anharmonic phonon-phonon scattering rates), increased bonding strength, and phonon group velocities. These results provide comprehensive insights into the phase-dependent electro-optical properties, highlighting their potential in optoelectronic devices. On top of that, the exceptional thermal conductivities and their tunable nature across the two polymorphic forms of ${\mathrm{ZrSi}}_2{\mathrm{N}}_4$ unlock exciting opportunities for designing advanced two-dimensional materials, offering ground-breaking potential in thermal management and heat dissipation technologies.

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• Density of states
• Electronic structure
• First-principles calculations
• Optoelectronics
• Phonons
• Thermal conductivity