Effect of Zn:Sn stoichiometry on the morphological and electrical properties of Aerosol Deposited ZnSnO Films

Abstract

Zinc tin oxide (ZnSnO) is a ternary oxide semiconductor that has gained increasing attention due to its wide band gap, typically around 3.5 to 4.0 eV, depending on the specific stoichiometry of the material, good transparency in the visible range, and potential for n-type conductivity. These characteristics make ZnSnO a promising candidate for applications including thin-film transistors, solar cells, and sensors [1]. ZnSnO combines the properties of its binary components, ZnO and SnO₂, offering enhanced control over electrical and optical behavior through stoichiometric tuning. Among the various deposition techniques, aerosol spray pyrolysis stands out as a cost-effective and scalable method for producing uniform thin films. In this study, we investigated the influence of Zn:Sn stoichiometric ratios (1:2 and 2:1) on the morphological and electrical properties of ZnSnO thin films deposited by aerosol spray onto p-type silicon substrates. Scanning electron microscopy (SEM) images revealed that the obtained samples exhibit uniform surface coverage, though the crystallite morphology significantly depends on the Zn:Sn ratio. For Zn:Sn = 2:1, well-defined crystallites with sizes ranging from 100–150 nm were observed. In contrast, the sample with Zn:Sn = 1:2 presented irregular, disordered structures. The current-voltage characteristics of the ZnSnO films was analyzed under both dark and illuminated conditions (100 mW/cm²). For the sample with Zn:Sn = 2:1, the semilogarithmic I–V plot demonstrated a saturation current Is = 8.8 mA and an ideality factor n = 2.6, suggesting a charge transport mechanism dominated by recombination in the depletion region, along with additional parasitic effects such as trap-assisted tunneling. Concerning Zn:Sn = 1:2, the extracted parameters were Is = 1.6 µA and n = 1.4, indicating a diffusion-dominated transport mechanism with contributions from junction recombination. Besides this, a higher saturation current (e.g., 8.8 mA) could be more efficient for applications where rapid photoresponse and high conductivity are more prioritized than detecting extremely low concentrations (e.g.,1.6 µA). These findings demonstrate that varying the Zn:Sn stoichiometry significantly influences both the morphology and electrical performance of ZnSnO films, enabling targeted optimization for specific device applications.