Cuprous oxide thin films obtained by spray-pyrolysis technique

Cu–O system thin films of 500 nm thickness were deposited on glass substrates by the spray-pyrolysis technique. The substrate temperatures (T_s) were in the 270–380 °C range with steps of 20 °C, including T_s = 340 °C. The precursor solution was obtained starting from copper nitrate (Cu(NO₃)₂), glucose (C₆H₁₂O₆) as reducing agent, and a deionized water-2 propanol mixture as solvent. XRD patterns revealed polycrystalline films with different phases depending on the T_s: (i) Cu₂O + Cu for 270 °C ≤ T_s ≤ 310 °C, (ii) Cu₂O for 330 °C ≤ T_s ≤ 340 °C and (iii) Cu₂O + CuO for 360 °C ≤ T_s≤380 °C. A crystallite size of 21 nm was obtained for cuprite phase (Cu₂O). Cu₂O films exhibited p type conductivity, electrical resistivity of 10² Ω-cm, electrical mobility 4.6 cm² V⁻¹s⁻¹ and major carrier concentration of 7.2 × 10¹⁵ cm⁻³. A maximum optical transmittance of 75% was obtained in the 650–800 nm range, with an abrupt absorption edge around 520 nm corresponding to the optical gap of 2.37 eV, which was calculated assuming the model for forbidden direct transition (n = 2/3). Uniform deposits and spherical aggregates of the order of 80 nm were observed using Field Emission Scanning Electronic Microscope.