Structural and optical properties of (TlInS₂)_0.75(TlInSe₂)_0.25 thin films deposited by thermal evaporation

Abstract

Layered semiconductor materials have become a serious research topic in recent years, thanks to their effective optical properties. In this article, the thin-film structure of Tl2In2S3Se [(TlInS2)(0.75)(TlInSe2)(0.25)] material with layered structure was grown by thermal evaporation method. The structural, morphological, and optical properties of the deposited thin films were examined. X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM) techniques were used to get information about structural and morphological properties of the thin films. XRD pattern presented well-defined peaks associated with monoclinic crystalline structure. The crystallite size, dislocation density, and lattice strain of the films were also obtained from the analyses of XRD pattern. EDS analysis showed that atomic compositional ratios of the Tl, In, S, and Se elements are consistent with chemical formula of Tl2In2S3Se. The optical characterization of thin film was performed using transmission and Raman spectroscopy techniques. Raman spectrum offered information about the vibrational modes of the thin film. The analyses of the transmission spectrum presented the indirect and direct band gap energies of the Tl2In2S3Se thin film as 2.23 and 2.52 eV, respectively. The further analyses on the absorption coefficient resulted in Urbach energy of 0.58 eV.