Characterization of structural, optical, sensing, and electrical implications of Mn-ion introducing in MnxSe75-xS25 thin films for optoelectronic and gas sensor applications

Abstract

This study investigates the impact of Mn-ion doping on various characteristics of thin films composed of MnxSe75-xS25. These films have a thickness of 170 nm and were tested at around 300 K with different levels of Mn doping, specifically at x = 0, 25, 50, and 75 wt%Mn. We employed techniques such as energy dispersive X-ray analysis EDXA to ascertain elemental composition, and both X-ray diffraction XRD, and scanning electron microscopy SEM to analyze the microstructure and morphology of the films. X-ray photoelectron spectroscopy XPS analyzed the surface chemistry of the 50 wt%Mn thin film, revealing polycrystalline structures in both Mn-doped and undoped films. Mn-doping enhanced photoluminescence, indicating reduced bandgap energy and a shift in peak towards longer wavelengths, implying lattice defects. All films exhibited two emission bands in the redshift region. The first, a high-intensity band, appeared (3.102–2.284 eV) between (400–543.2 nm). The second, a low-intensity band, was visible (1.978–2.398 eV) between (517.3–627.4 nm), indicating two distinct optical bandgap energies. Longer UV exposure increased photocurrent at 328 nm, correlating with Mn content. Various methods were used to determine optical parameters (Tauc and Urbach energies), confirming the presence of two distinct energy levels. Dispersion characteristics in low- and high-energy bands were analyzed from linear optical properties. When exposed to reducing gas (CO), film resistance decreased, indicating n-type semiconductor behavior. This novel study enhances our understanding of Mn-Se-S thin films and their potential use in optoelectronic and gas sensor applications.