Electronic properties and thermoelectric performance of 2D ZnSe and its haeckelite phases by first-principles approach and Boltzmann transport theory

Abstract The electronic and thermoelectric properties of two-dimensional (2D) ZnSe and its Haeckelite phase were investigated using first-principles calculations and Boltzmann transport theory within the constant relaxation time approximation. We found the pristine 2D ZnSe as an n-type semiconductor with a 1.70 eV band gap, which widens under compressive strain and narrows under tensile strain. The Haeckelite phase exhibits degenerate n-type semiconductor behaviour with a 1.29 eV band gap. Thermoelectric efficiencies were evaluated through the transport coefficients and the associated figure of merit (ZT). The pristine and compressed ZnSe demonstrate improved thermoelectric efficiency at moderate through high temperatures, achieving ZT values up to 0.96 and 0.97 at 400 K, respectively, while stretched ZnSe reaches a ZT of 1.07 at 800 K. The Haeckelite materials show consistent thermoelectric behaviour with moderate ZT values. The results showed that strain and phase engineering are effective tools to optimize thermoelectric efficiency in 2D ZnSe and Haeckelite materials.