Effects of iron incorporation on the properties of tin sulfide thin films: a multi-technique investigation

Abstract

This study presents a systematic investigation into the effects of iron (Fe) incorporation (pure, 15, 25, 35, and 45 at%) on the structural, morphological, and optical properties of tin sulfide (SnS) thin films. A multi-technique approach employing X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy was used for characterization. XRD analysis confirmed the orthorhombic phase of SnS in undoped films and revealed a lattice contraction at lower Fe concentrations (≤25 at%) due to successful substitutional doping. At higher concentrations (≥35 at%), the formation of secondary phases, identified as FeS2 and Sn2S3, was observed, leading to degraded crystallinity. SEM and TEM analyses corroborated these findings, showing a transition from a dense, homogeneous morphology to a rough, agglomerated surface with distinct secondary phase nanoparticles at 45 at% Fe. EDX mapping confirmed homogeneous element distribution at lower doping levels and Fe clustering at higher levels. PL spectroscopy demonstrated a blue shift in the emission peak at intermediate doping levels (25 at%), attributed to the Burstein-Moss effect from increased charge carriers. However, severe PL quenching and the emergence of deep-level emissions occurred at higher Fe concentrations (35 and 45 at%), indicating the introduction of non-radiative recombination centers. The results conclusively identify an optimal Fe incorporation threshold near 25 at%, beyond which the beneficial properties of SnS are significantly compromised by phase segregation and defect generation. This work provides critical insights for tailoring Fe-doped SnS properties for optoelectronic applications.