Novel synthesis of multiphase Cu–Fe–Se semiconductor films by cathodic cylinder plasma deposition: influence of deposition temperature on optoelectrical properties

The deposition of thin films containing Cu, Fe, and Se has been widely investigated due to their potential applications in optoelectronics and thermoelectrics. In this study, multiphase Cu–Fe–Se thin films were deposited by cathodic cylinder plasma deposition (CCyPD) at 400, 450, and 500 °C to investigate how temperature-dependent changes in crystalline phase assemblage and film morphology relate to their optical and electrical properties. Structural characterization was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), revealing a transition from the β-FeSe phase to the δ-FeSe phase and an increase in the presence of Cu 2 Se and Fe 7 Se 8 with rising temperature. Diffuse reflectance spectroscopy showed low reflectance across the entire spectral range (<8%), with the lowest value observed for films deposited at 500 °C (<4.6%). The reduction of the band gap with increasing temperature (from 1.42 eV at 400 °C to 1.04 eV at 500 °C) was accompanied by a decrease in sheet resistivity, indicating enhanced electrical conductivity. The extinction coefficient indicated that, although the films deposited at 400 and 450 °C exhibited higher intrinsic absorption, the 500 °C film showed the highest overall absorption, highlighting the role of morphology in light interactions. This behavior, combined with low reflectance and reduced sheet resistivity, suggests that the films deposited at 500 °C present promising characteristics for optoelectronic applications, such as solar cells and photonic sensors.