Optimization of Zn2SnO4 thin film by post oxidation of thermally evaporated alternate Sn and Zn metallic multi-layers

Abstract

An attempt to optimize Zn2SnO4 (ZTO) thin film has been done by alternate thermal evaporation of ‘Sn’ and ‘Zn’ in the sequence Sn10/Zn15/Sn15/Zn15/Sn5 onto corning glass substrates and subsequent post oxidation process. The XRD patterns of as-deposited metallic thin films changed over from metallic to oxidized ZTO phase with cubic spinel structure along with ZnO phase. The film thickness and roughness increased apparently due to diffusion of oxygen into the metallic inter-layers. The binding energies estimated from the XPS data also indicated oxidation of the metallic multi-layers. Post-annealing of the film developed transparency in visible region to around 40%. The direct band gap of ZTO and ZnO were estimated to be 3.46 eV and 3.10 eV respectively. The annealed ZTO thin film was measured for electrical transport parameters by Hall Effect measurement. Raman spectrum observed at 668 cm−1 is due to stretching vibration of short metal-oxide bonds in the MO6 octahedron. The photoluminescence spectrum showed blue emission centered around 436 nm predominantly due to oxygen vacancies in addition to weak orange emission centered at 625 nm. Gas sensor using thin films of as-deposited and ZTO formed by post-annealing process showed significant sensing response for NO2 gas. These results reveal that the ZTO thin film deposited by alternate thermal evaporation and subsequent post oxidation is worth exploring as transparent conducting electrode and also as a gas sensing material.