Correlating Optical, Electrical, and Structural Properties of Selenium Thin Films with Thickness and Temperature

This study systematically investigates the optical, electrical, and structural properties of thermally evaporated selenium (Se) thin films with thicknesses of 60, 80, and 100 nm under varying thermal conditions. UV-Vis spectroscopy reveals strong absorption in the visible region with a clear dependence on film thickness and annealing temperature. The optical band gap decreases from approximately 2.10 eV for 60 nm films to 1.95 eV for 100 nm films and further narrows upon thermal annealing, indicating enhanced structural ordering. Thicker films exhibit higher absorbance and a red shift in the absorption edge due to reduced disorder and improved crystallinity. Raman spectroscopy confirms the presence of characteristic Se-Se vibrational modes and reveals enhanced structural ordering with increasing thickness. Electrical measurements demonstrate a transition from ohmic conduction at room temperature to trap-assisted space-charge-limited conduction (SCLC) at elevated temperatures. The conductivity increases significantly with both film thickness and annealing temperature owing to thermally activated carrier transport and improved film connectivity. These findings establish strong correlations between structural ordering, optical band-gap modulation, and charge transport in selenium thin films, highlighting their potential for photovoltaic, photodetector, and thermally responsive optoelectronic applications.