Effect of samarium addition on physical and electrical properties of copper oxide thin films

In this research, samarium (Sm)-doped copper oxide (CuO) samples were successfully fabricated on soda-lime glass substrates using the spin coating method, with Sm concentrations of 0, 1, 2, and 3 weight percent. The primary objective was to examine how varying levels of Sm doping influence the structural, topological, and optical characteristics of CuO. Structural evaluation conducted via X-ray diffraction (XRD) confirmed that the obtained samples exhibit a polycrystalline structure, predominantly oriented along the (-111) crystallographic plane. Crystallite size (D_hkl), interplaner distance (d_hkl), dislocation density (δ_hkl), full width at half maximum (β_hkl), and micro-strain (ε_hkl) for the Sm-doped CuO samples were evaluated related to the XRD data. For the (-111) plane, crystallite size decreased from 30.04 nm to 16.52 nm, dislocation density increased from 11.08 × 1014 m-2 to 36.66 × 1014 m-2, and microstrain increased from 4.01 × 10-4 to 7.12 × 10-4. Similarly, for the (200) plane, crystallite size decreased from 27.78 nm to 15.21 nm, dislocation density increased from 12.96 × 1014 m-2 to 43.25 × 1014 m-2, and microstrain increased from 4.22 × 10-3 to 7.12 × 10-3. Morphologically, CuO exhibited a quasi-spherical shape with small agglomerations. Surface analyses demonstrated that Sm doping significantly altered the CuO film morphology. Optical characterizations were conducted using UV–Vis measurement system. The findings demonstrated that samarium doping significantly influenced the band gap value of CuO samples. The estimated band gap values were 1.80 eV for the undoped sample, increasing progressively to 1.90 eV, 2.10 eV, and 2.20 eV for the films doped with 1%, 2%, and 3% Sm, respectively. These outcomes reveal a notable widening of the band gap as the Sm doping concentration upsurges from 0% to 3%. The dielectric constants and refractive indices of both pure and Sm-doped CuO samples were estimated using theoretical models proposed by Moss relation, Hervé & Vandamme relation, and Ravindra relation. The consistency among these methods confirms the reliability of the optical characterization. The study also revealed an inverse relationship between the absorption coefficient and particle size, where Sm doping resulted in smaller crystallite sizes and a consistent reduction in the absorption coefficient. The pure CuO film displayed a distinct peak within the visible spectrum compared to the other CuO samples, suggesting enhanced light absorption in that wavelength region. The high crystallinity of the undoped CuO promoted absorption of greater photon energies (hν) in the visible spectrum, contributing to enhanced optical conductivity value at lower energy band. Consequently, the undoped CuO showed higher light absorption efficiency in the visible region. In contrast, Sm-doped CuO samples demonstrated reduced photon absorption and correspondingly lower optical conductivity. In summary, this study demonstrates that Sm doping significantly influences the structural, topological, and optical characteristics of CuO samples. The results indicate that while undoped CuO exhibits greater optical conductivity within the visible range, the incorporation of Sm alters the material's optical properties in ways that make the doped films promising candidates for use in optoelectronic devices and solar energy applications. The electrical characterization of the n-Si/CuO/Ag heterojunction diode revealed the following parameters resulting from the ln(I)-V plot: for the undoped CuO diode, the ideality factor was 2.84, barrier height was 0.793 eV, and leakage current was 5.4 × 10-8 A; for the 1% Sm-doped CuO diode, n = 1.99, barrier height 0.73 eV, and leakage current 7.1 × 10-7 A; for the 2% Sm-doped CuO diode, n = 2.84 and barrier height 0.793 eV; and for the 3% Sm-doped CuO diode, n = 2.57, barrier height 0.725 eV, and leakage current 6.19 × 10-9 A.