Synthesis, Growth and Characterization of Tunable Band Gap Nanostructured Copper(I) Oxide (Cu₂O) Semiconductor

The bulk nanostructured copper(I) oxide (Cu₂O) has been successfully prepared by a new modified wet chemical route and thermal annealing of copper(II) oxide (CuO) pellets at reduced atmospheric pressure of 10⁻² torr in the temperature range between 600–650 °C, which seems to be first of its kind to the best of our knowledge. The gross structure/phase identification of as synthesized copper oxides by powder X-ray diffraction (XRD) technique shows the formation of single phase of cupric oxide as well as cuprous oxide depending upon the annealing conditions i.e., temperature, pressure and time. The structural/micro-structural characteristics of copper oxides (Cu₂O) explored by the scanning electron microscopy (SEM), atomic force microscopic (AFM) and transmission electron microscopy (TEM) reveals the formation of nanospheres (≈50 nm) and nanorods (≈100 to 200 nm) of copper(I) oxide. The surface characterization of the as-annealed Cu₂O pellets at reduced atmospheric pressure of 10⁻² torr at temperature of 650 °C by SEM have further shown the occurrence of curious growth characteristics resembling spiral like features. The band gap energy (E _g) of these cuprous oxides, determined from the electrical resistivity (ρ) measurement by the four-probe method as a function of temperatures ranging from 300 K to 500 K is found to be varying between 2.2±0.5 eV. The room temperature (RT) photoluminescence (PL) spectra in both emission and excitation modes of nanostructured Cu₂O shows two spectral emission at λ = 388.2 nm (E = 3.187 eV) in red band and λ = 753.15 nm (E = 1.64 eV) in orange band as well as strong and weak excitation peaks at λ = 242.70 nm (E = 5.09 eV) and λ = 223.71 nm (E = 5.53 eV) respectively. All the above peaks are the characteristic of cuprous oxides (Cu₂O).