Structure and Optical Band Gap of Inverse Spinel Zn2SnO4 Epitaxial Films

Abstract

Inverse spinel Zn2SnO4 (ZTO) films have been grown on MgO(001) and MgAl2O4(001) substrates by pulsed laser deposition. Detailed structural investigation by high-resolution X-ray diffraction, including conventional θ–2θ linear scans, φ scans and reciprocal space mappings, revealed the epitaxial characteristics of the ZTO films. Meanwhile, the in-plane and out-of-plane lattice parameters were extracted to be about a = b=8.615 A and c = 8.629 A from the symmetry and asymmetry reflections. The surface morphologies of ZTO films were examined by atomic force microscopy, and all the films exhibit very smooth surfaces. X-ray photoelectron spectroscopy measurement was taken to disclose the oxidation states of elements. The optical properties of ZTO films were probed by measuring the optical transmittances. The band gaps of ZTO films grown on MgO(001) and MgAl2O4(001) were extracted to be 4.26 eV and 4.30 eV by extrapolating the absorption edge, respectively. Theoretically, the band structure was also calculated using density functional theory. The results show that ZTO film is a direct band gap semiconductor with the band gap value of 2.64 eV. Such a wide band gap semiconductor with an inverse spinel structure should be of high interest for epitaxial heterojunction and optical device application.