Physical, photochemical, and extended piezoelectric studies of orthorhombic ZnSnN2 nanocolumn arrays

Abstract This study reports the piezo-related properties of ZnSnN2 (ZTN) fabricated through natural Sn3N4 and Zn thickness gradients deposited oppositely on a fluorine-doped tin oxide substrate to form Zn–Sn3N4 composition spreads to enhance the relative variation of the cation ratios and to promote the formation of orthorhombic ZTN. No moving shutter was incorporated into combinatorial magnetron sputtering to minimize fabrication complexity. The Sn3N4-rich deposition (Location 1) of the Zn–Sn3N4 composition spread exhibited Sn3N4 and the single crystallinity of orthorhombic (Pna21) ZTN nanocolumn arrays, which grew along the [0 0 1] direction, confirmed by locked-coupled X-ray diffraction and transmission electron microscopy. The constituent element diffusion and variation of the atomic binding state of constituent elements along the substrate normal were tracked by depth profiling using secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. The band gap of ZTN (approximately 2.0 eV) was estimated from a UV–vis spectrum. The piezotronic and piezophototronic effects of ZTN were determined through a facile current–voltage measurement, which were explained by the Schottky barrier height variations. Piezophotocatalysis exhibited the highest rate constant (k, approximately 9 × 10−3/min) of the measurements, which was attributed to the reduced recombination of the photogenerated e−–h+ pairs because of the piezopotential distribution. Additionally, O2− radicals were predominately indicated in the degradation process.