Impact of surface morphology and thickness of tin selenide thin films on their optical properties

Abstract

Thin tin selenide (SnSe) films were synthesized on polyamide sheets via the two-stage adsorption/diffusion method. The surface morphology and chemical composition of the hereby obtained thin film were characterized by energy-dispersive spectroscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray photoemission spectroscopy techniques. The X-ray diffraction analysis showed that the obtained films are chemically close to tin selenide with three orthorhombic phases. A systematic investigation was carried out to understand the factors of the next stage process, the influence of conditions on the structure, the surface morphology of SnSe thin films, and their thickness. It was found that the concentration of tin(II) precursor solution, its pH value, and temperature led to the creation of films of various thickness and surfaces with different features. The SnSe films consisted of nanoscale ∼40 nm size grains, which in turn were combined into agglomerates of up to 100 nm to 3 µm. The stoichiometric ratios of tin and selenium in SnSe films were also dependent on the next-stage conditions of the synthesis process. The thickness of the SnSe films and the size of the crystallites of which they are composed have a decisive influence on the optical properties of these layers and the band gap of which varied in the range of 1.75–1.24 eV.