Controlled growth, structure and optical properties of Fe-doped cubic π- SnS thin films

In this paper, the structural, surface morphology and optical properties of Fe-doped cubic tin sulfide (π-SnS) films are reported. The Fe-doped (0.0-10.0 by wt.% Fe in SnS) π-SnS films are grown on glass substrate by chemical bath deposition. Microstructural and optical properties of all films are studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-Vis/NIR spectroscopy. XRD spectra confirm the formation of single phase in all Fe-doped SnS films. All Fe-doped SnS films exhibit simple cubic (π-SnS) phase. The crystallite size decreases (40 ± 2 nm - 23 ± 1 nm) with the increase in Fe-concentration. FTIR spectra indicate the Sn-S bond stretching around 863.47 cm−1, 750.39 cm−1 and 554.50 cm−1. Surface AFM images reveal a uniform distribution of spherical grains (in 0.0% Fe doped π-SnS film) with small voids. However, formation of small clusters and nucleation of islands are observed in all Fe-doped π-SnS films. All films have high absorption coefficient (α ∼ 104 cm−1). From optical measurements, all films are found to exhibit direct band gap, Eg. The calculated band gap, Eg is found to decrease (1.74 eV-1.63 eV) with increasing Fe-concentration. The results indicate that the Eg is possible to tune (over a narrow range) for optical device applications by controlling the microstructure and phase of Fe-doped π-SnS films.