Polarization-Driven Type-II and Z-Scheme Heterojunctions in GaN/ZrSO and GaN/ZrS₂ for Enhanced Photocatalysis

In this work, the structural stability, electronic properties, and photocatalytic performance of three heterostructures─nonpolar/nonpolar GaN/ZrS2 and nonpolar/polar GaN/ZrSO with different polarization directions (P↑ and P↓)─were systematically investigated using first-principles calculations. The GaN/ZrS2 heterostructure was found to form a direct Z-scheme junction, with efficient charge separation driven by a built-in electric field. This internal field enhances the redox potential, making the GaN/ZrS2 heterostructure highly suitable for overall photocatalytic water splitting. In contrast, the P↓ GaN/ZrSO heterostructure was shown to exhibit type II band alignment, where the presence of an intrinsic polarization field from the ZrSO monolayer further boosts its hydrogen evolution efficiency. Both GaN/ZrS2 and P↓ GaN/ZrSO heterostructures demonstrated strong light absorption in the visible spectrum and favorable band-edge positions for redox reactions. Thermodynamic calculations of Gibbs free energy confirmed that spontaneous water splitting can occur under neutral conditions for both systems. Additionally, dielectric function analysis revealed enhanced visible light absorption, especially in the P↓ GaN/ZrSO system. These results indicate that GaN-based heterostructures offer significant potential as efficient and stable photocatalysts for water splitting, with the ability to harness visible light and optimize charge carrier dynamics through polarization effects. This study highlights the promise of these heterostructures for advancing sustainable energy applications.