High out-of-plane piezoelectric response in Janus SeWZH (Z = N, P, As) semiconductors: a first-principles prediction

A systematic first-principles investigation has been conducted to explore the fundamental properties of Janus SeWZH (Z = N, P, As) monolayers. Cohesive-energy calculations, phonon-dispersion analysis, and ab initio molecular dynamics simulations consistently verify the energetic, dynamical, and thermal stabilities of the proposed SeWNH, SeWPH, and SeWAsH monolayers, indicating their potential feasibility for experimental synthesis. Electronic structure calculations reveal semiconducting behavior for all SeWZH monolayers, with band gaps between 1.59 and 2.61 eV at the HSE06 theoretical level. Specifically, SeWNH is identified as an indirect-band-gap semiconductor, whereas SeWPH and SeWAsH possess direct band gaps. Structural asymmetry induces in-plane and out-of-plane piezoelectricity, with the highest out-of-plane coefficient d ₃₁ = 0.51 pm V^-1 obtained for SeWNH. Furthermore, spin-orbit coupling drives significant spin splitting at the valence band K valley. Charge transport analysis reveals that acoustic deformation potential scattering dominates, resulting in low carrier mobilities. The predicted low carrier mobilities reflect the strong influence of intrinsic scattering on charge transport.